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 $93.33   5.361%   $98.3334   $98.33   $98.35   $98.30  
  Purchase #2 $88.59   6.568%   $94.4086   $94.41   $94.40   $94.40  
  Purchase #3 $234.59   11.855%   $262.4006   $262.40   $262.40   $262.40  
  Purchase #4 $32.54   6.853%   $34.77   $34.77   $34.75   $34.80  
  Purchase #5 $112.51   11.784%   $125.7682   $125.77   $125.75   $125.80  
  Purchase #6 $246.74   3.438%   $255.2229   $255.22   $255.20   $255.20  
  Purchase #7 $93.52   5.433%   $98.6009   $98.60   $98.60   $98.60  
  7 purchase totals = $901.82       $969.5046   $969.50   $969.45   $969.50