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 $46.49   12.567%   $52.3324   $52.33   $52.35   $52.30  
  Purchase #2 $66.81   8.414%   $72.4314   $72.43   $72.45   $72.40  
  Purchase #3 $113.96   8.708%   $123.8836   $123.88   $123.90   $123.90  
  Purchase #4 $216.28   5.696%   $228.5993   $228.60   $228.60   $228.60  
  Purchase #5 $125.49   5.186%   $131.9979   $132.00   $132.00   $132.00  
  Purchase #6 $230.35   6.445%   $245.1961   $245.20   $245.20   $245.20  
  Purchase #7 $95.81   8.812%   $104.2528   $104.25   $104.25   $104.30  
  7 purchase totals = $895.19       $958.6935   $958.69   $958.75   $958.70