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 $61.86   4.833%   $64.8497   $64.85   $64.85   $64.80  
  Purchase #2 $119.66   5.267%   $125.9625   $125.96   $125.95   $126.00  
  Purchase #3 $205.51   13.149%   $232.5325   $232.53   $232.55   $232.50  
  Purchase #4 $184.98   13.383%   $209.7359   $209.74   $209.75   $209.70  
  Purchase #5 $218.88   12.738%   $246.7609   $246.76   $246.75   $246.80  
  Purchase #6 $247.98   9.219%   $270.8413   $270.84   $270.85   $270.80  
  Purchase #7 $111.60   13.378%   $126.5298   $126.53   $126.55   $126.50  
  7 purchase totals = $1,150.47       $1,277.2126   $1,277.21   $1,277.25   $1,277.10