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 $76.61   4.763%   $80.2589   $80.26   $80.25   $80.30  
  Purchase #2 $215.91   13.315%   $244.6584   $244.66   $244.65   $244.70  
  Purchase #3 $89.90   12.813%   $101.4189   $101.42   $101.40   $101.40  
  Purchase #4 $112.48   9.686%   $123.3748   $123.37   $123.35   $123.40  
  Purchase #5 $42.33   12.488%   $47.6162   $47.62   $47.60   $47.60  
  Purchase #6 $149.48   3.462%   $154.655   $154.66   $154.65   $154.70  
  Purchase #7 $13.41   7.424%   $14.4056   $14.41   $14.40   $14.40  
  7 purchase totals = $700.12       $766.3878   $766.40   $766.30   $766.50