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 $62.52   11.443%   $69.6742   $69.67   $69.65   $69.70  
  Purchase #2 $174.33   8.281%   $188.7663   $188.77   $188.75   $188.80  
  Purchase #3 $104.46   5.677%   $110.3902   $110.39   $110.40   $110.40  
  Purchase #4 $158.39   7.652%   $170.51   $170.51   $170.50   $170.50  
  Purchase #5 $63.40   7.409%   $68.0973   $68.10   $68.10   $68.10  
  Purchase #6 $246.62   11.229%   $274.313   $274.31   $274.30   $274.30  
  Purchase #7 $5.84   8.641%   $6.3446   $6.34   $6.35   $6.30  
  7 purchase totals = $815.56       $888.0956   $888.09   $888.05   $888.10