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 $93.25   11.860%   $104.3095   $104.31   $104.30   $104.30  
  Purchase #2 $182.69   9.137%   $199.3824   $199.38   $199.40   $199.40  
  Purchase #3 $81.66   5.714%   $86.3261   $86.33   $86.35   $86.30  
  Purchase #4 $150.42   13.203%   $170.28   $170.28   $170.30   $170.30  
  Purchase #5 $5.80   8.816%   $6.3113   $6.31   $6.30   $6.30  
  Purchase #6 $132.88   3.437%   $137.4471   $137.45   $137.45   $137.40  
  Purchase #7 $82.25   13.466%   $93.3258   $93.33   $93.35   $93.30  
  7 purchase totals = $728.95       $797.3822   $797.39   $797.45   $797.30