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 $63.43   5.476%   $66.9034   $66.90   $66.90   $66.90  
  Purchase #2 $143.97   3.865%   $149.5344   $149.53   $149.55   $149.50  
  Purchase #3 $31.48   11.107%   $34.9765   $34.98   $35.00   $35.00  
  Purchase #4 $239.70   8.670%   $260.482   $260.48   $260.50   $260.50  
  Purchase #5 $152.40   5.605%   $160.942   $160.94   $160.95   $160.90  
  Purchase #6 $138.73   13.437%   $157.3712   $157.37   $157.35   $157.40  
  Purchase #7 $92.55   10.115%   $101.9114   $101.91   $101.90   $101.90  
  7 purchase totals = $862.26       $932.1209   $932.11   $932.15   $932.10