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 $59.74   4.354%   $62.3411   $62.34   $62.35   $62.30  
  Purchase #2 $234.48   12.406%   $263.5696   $263.57   $263.55   $263.60  
  Purchase #3 $96.72   5.221%   $101.7698   $101.77   $101.75   $101.80  
  Purchase #4 $145.80   12.552%   $164.1008   $164.10   $164.10   $164.10  
  Purchase #5 $126.71   13.553%   $143.883   $143.88   $143.90   $143.90  
  Purchase #6 $43.83   7.197%   $46.9844   $46.98   $47.00   $47.00  
  Purchase #7 $92.67   5.828%   $98.0708   $98.07   $98.05   $98.10  
  7 purchase totals = $799.95       $880.7195   $880.71   $880.70   $880.80