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 $117.61   11.153%   $130.727   $130.73   $130.75   $130.70  
  Purchase #2 $203.25   6.121%   $215.6909   $215.69   $215.70   $215.70  
  Purchase #3 $81.92   12.323%   $92.015   $92.02   $92.00   $92.00  
  Purchase #4 $146.71   12.813%   $165.508   $165.51   $165.50   $165.50  
  Purchase #5 $228.47   7.659%   $245.9685   $245.97   $245.95   $246.00  
  Purchase #6 $48.79   3.406%   $50.4518   $50.45   $50.45   $50.50  
  Purchase #7 $36.79   10.469%   $40.6415   $40.64   $40.65   $40.60  
  7 purchase totals = $863.54       $941.0027   $941.01   $941.00   $941.00