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 $60.71   8.185%   $65.6791   $65.68   $65.70   $65.70  
  Purchase #2 $129.95   10.792%   $143.9742   $143.97   $143.95   $144.00  
  Purchase #3 $8.42   9.165%   $9.1917   $9.19   $9.20   $9.20  
  Purchase #4 $58.85   11.366%   $65.5389   $65.54   $65.55   $65.50  
  Purchase #5 $149.55   11.838%   $167.2537   $167.25   $167.25   $167.30  
  Purchase #6 $110.39   8.152%   $119.389   $119.39   $119.40   $119.40  
  Purchase #7 $133.32   6.433%   $141.8965   $141.90   $141.90   $141.90  
  7 purchase totals = $651.19       $712.9231   $712.92   $712.95   $713.00