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 $151.85   11.322%   $169.0425   $169.04   $169.05   $169.00  
  Purchase #2 $226.95   11.500%   $253.0493   $253.05   $253.05   $253.00  
  Purchase #3 $243.96   6.134%   $258.9245   $258.92   $258.90   $258.90  
  Purchase #4 $195.71   5.872%   $207.2021   $207.20   $207.20   $207.20  
  Purchase #5 $124.41   12.446%   $139.8941   $139.89   $139.90   $139.90  
  Purchase #6 $208.30   3.303%   $215.1801   $215.18   $215.20   $215.20  
  Purchase #7 $9.90   4.724%   $10.3677   $10.37   $10.35   $10.40  
  7 purchase totals = $1,161.08       $1,253.6603   $1,253.65   $1,253.65   $1,253.60