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 $56.37   8.234%   $61.0115   $61.01   $61.00   $61.00  
  Purchase #2 $101.54   5.532%   $107.1572   $107.16   $107.15   $107.20  
  Purchase #3 $80.92   5.607%   $85.4572   $85.46   $85.45   $85.50  
  Purchase #4 $125.69   8.563%   $136.4528   $136.45   $136.45   $136.50  
  Purchase #5 $131.65   8.313%   $142.5941   $142.59   $142.60   $142.60  
  Purchase #6 $118.44   13.290%   $134.1807   $134.18   $134.20   $134.20  
  Purchase #7 $90.38   13.445%   $102.5316   $102.53   $102.55   $102.50  
  7 purchase totals = $704.99       $769.3851   $769.38   $769.40   $769.50