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 $185.68   6.454%   $197.6638   $197.66   $197.65   $197.70  
  Purchase #2 $68.70   12.240%   $77.1089   $77.11   $77.10   $77.10  
  Purchase #3 $117.40   5.276%   $123.594   $123.59   $123.60   $123.60  
  Purchase #4 $168.61   9.845%   $185.2097   $185.21   $185.20   $185.20  
  Purchase #5 $40.35   13.452%   $45.7779   $45.78   $45.80   $45.80  
  Purchase #6 $188.38   4.821%   $197.4618   $197.46   $197.45   $197.50  
  Purchase #7 $67.76   12.448%   $76.1948   $76.19   $76.20   $76.20  
  7 purchase totals = $836.88       $903.0109   $903.00   $903.00   $903.10