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 $60.45   10.267%   $66.6564   $66.66   $66.65   $66.70  
  Purchase #2 $30.75   5.469%   $32.4317   $32.43   $32.45   $32.40  
  Purchase #3 $108.59   4.583%   $113.5667   $113.57   $113.55   $113.60  
  Purchase #4 $244.65   9.785%   $268.589   $268.59   $268.60   $268.60  
  Purchase #5 $31.73   5.259%   $33.3987   $33.40   $33.40   $33.40  
  Purchase #6 $141.75   9.237%   $154.8434   $154.84   $154.85   $154.80  
  Purchase #7 $125.29   9.241%   $136.868   $136.87   $136.85   $136.90  
  7 purchase totals = $743.21       $806.3539   $806.36   $806.35   $806.40