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 $215.53   9.480%   $235.9622   $235.96   $235.95   $236.00  
  Purchase #2 $228.27   8.134%   $246.8375   $246.84   $246.85   $246.80  
  Purchase #3 $10.53   13.459%   $11.9472   $11.95   $11.95   $11.90  
  Purchase #4 $133.88   13.112%   $151.4343   $151.43   $151.45   $151.40  
  Purchase #5 $170.34   12.739%   $192.0396   $192.04   $192.05   $192.00  
  Purchase #6 $242.29   9.469%   $265.2324   $265.23   $265.25   $265.20  
  Purchase #7 $170.39   7.191%   $182.6427   $182.64   $182.65   $182.60  
  7 purchase totals = $1,171.23       $1,286.0959   $1,286.09   $1,286.15   $1,285.90