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 $208.35   13.703%   $236.9002   $236.90   $236.90   $236.90  
  Purchase #2 $247.96   4.853%   $259.9935   $259.99   $260.00   $260.00  
  Purchase #3 $157.87   11.814%   $176.5208   $176.52   $176.50   $176.50  
  Purchase #4 $87.73   7.276%   $94.1132   $94.11   $94.10   $94.10  
  Purchase #5 $72.32   3.545%   $74.8837   $74.88   $74.90   $74.90  
  Purchase #6 $67.38   9.705%   $73.9192   $73.92   $73.90   $73.90  
  Purchase #7 $158.54   13.496%   $179.9366   $179.94   $179.95   $179.90  
  7 purchase totals = $1,000.15       $1,096.2672   $1,096.26   $1,096.25   $1,096.20