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 $202.45   11.652%   $226.0395   $226.04   $226.05   $226.00  
  Purchase #2 $22.53   7.867%   $24.3024   $24.30   $24.30   $24.30  
  Purchase #3 $117.99   12.344%   $132.5547   $132.55   $132.55   $132.60  
  Purchase #4 $231.83   10.557%   $256.3043   $256.30   $256.30   $256.30  
  Purchase #5 $173.88   13.713%   $197.7242   $197.72   $197.70   $197.70  
  Purchase #6 $142.59   10.830%   $158.0325   $158.03   $158.05   $158.00  
  Purchase #7 $249.32   10.302%   $275.0049   $275.00   $275.00   $275.00  
  7 purchase totals = $1,140.59       $1,269.9625   $1,269.94   $1,269.95   $1,269.90