Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $177.54   13.756%   $201.9624   $201.96   $201.95   $202.00  
  Purchase #2 $222.85   8.474%   $241.7343   $241.73   $241.75   $241.70  
  Purchase #3 $104.58   11.286%   $116.3829   $116.38   $116.40   $116.40  
  Purchase #4 $91.70   10.829%   $101.6302   $101.63   $101.65   $101.60  
  Purchase #5 $160.38   12.831%   $180.9584   $180.96   $180.95   $181.00  
  Purchase #6 $96.46   12.711%   $108.721   $108.72   $108.70   $108.70  
  Purchase #7 $244.33   8.596%   $265.3326   $265.33   $265.35   $265.30  
  7 purchase totals = $1,097.84       $1,216.7218   $1,216.71   $1,216.75   $1,216.70