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 $86.32   7.610%   $92.889   $92.89   $92.90   $92.90  
  Purchase #2 $9.74   11.309%   $10.8415   $10.84   $10.85   $10.80  
  Purchase #3 $134.71   7.626%   $144.983   $144.98   $145.00   $145.00  
  Purchase #4 $133.79   5.355%   $140.9545   $140.95   $140.95   $141.00  
  Purchase #5 $92.44   3.120%   $95.3241   $95.32   $95.30   $95.30  
  Purchase #6 $221.39   11.273%   $246.3473   $246.35   $246.35   $246.30  
  Purchase #7 $187.34   8.842%   $203.9046   $203.90   $203.90   $203.90  
  7 purchase totals = $865.73       $935.2440   $935.23   $935.25   $935.20