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 $112.96   6.458%   $120.255   $120.26   $120.25   $120.30  
  Purchase #2 $61.59   11.511%   $68.6796   $68.68   $68.70   $68.70  
  Purchase #3 $73.74   10.476%   $81.465   $81.47   $81.45   $81.50  
  Purchase #4 $229.50   8.770%   $249.6272   $249.63   $249.65   $249.60  
  Purchase #5 $217.43   5.830%   $230.1062   $230.11   $230.10   $230.10  
  Purchase #6 $149.30   11.568%   $166.571   $166.57   $166.55   $166.60  
  Purchase #7 $105.87   10.462%   $116.9461   $116.95   $116.95   $116.90  
  7 purchase totals = $950.39       $1,033.6501   $1,033.67   $1,033.65   $1,033.70