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 $55.94   8.293%   $60.5791   $60.58   $60.60   $60.60  
  Purchase #2 $197.63   9.261%   $215.9325   $215.93   $215.95   $215.90  
  Purchase #3 $177.34   7.630%   $190.871   $190.87   $190.85   $190.90  
  Purchase #4 $127.52   10.872%   $141.384   $141.38   $141.40   $141.40  
  Purchase #5 $126.62   11.139%   $140.7242   $140.72   $140.70   $140.70  
  Purchase #6 $87.36   5.786%   $92.4146   $92.41   $92.40   $92.40  
  Purchase #7 $28.48   9.171%   $31.0919   $31.09   $31.10   $31.10  
  7 purchase totals = $800.89       $872.9973   $872.98   $873.00   $873.00