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 $58.42   10.561%   $64.5897   $64.59   $64.60   $64.60  
  Purchase #2 $209.59   3.317%   $216.5421   $216.54   $216.55   $216.50  
  Purchase #3 $182.98   11.329%   $203.7098   $203.71   $203.70   $203.70  
  Purchase #4 $70.54   4.187%   $73.4935   $73.49   $73.50   $73.50  
  Purchase #5 $80.37   5.620%   $84.8868   $84.89   $84.90   $84.90  
  Purchase #6 $197.63   4.716%   $206.9502   $206.95   $206.95   $207.00  
  Purchase #7 $61.76   11.241%   $68.7024   $68.70   $68.70   $68.70  
  7 purchase totals = $861.29       $918.8745   $918.87   $918.90   $918.90