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 $104.97   8.382%   $113.7686   $113.77   $113.75   $113.80  
  Purchase #2 $211.34   11.329%   $235.2827   $235.28   $235.30   $235.30  
  Purchase #3 $150.93   4.824%   $158.2109   $158.21   $158.20   $158.20  
  Purchase #4 $236.98   3.270%   $244.7292   $244.73   $244.75   $244.70  
  Purchase #5 $57.43   7.421%   $61.6919   $61.69   $61.70   $61.70  
  Purchase #6 $58.59   3.239%   $60.4877   $60.49   $60.50   $60.50  
  Purchase #7 $5.31   10.744%   $5.8805   $5.88   $5.90   $5.90  
  7 purchase totals = $825.55       $880.0515   $880.05   $880.10   $880.10