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 $47.74   12.493%   $53.7042   $53.70   $53.70   $53.70  
  Purchase #2 $101.72   13.274%   $115.2223   $115.22   $115.20   $115.20  
  Purchase #3 $244.29   4.708%   $255.7912   $255.79   $255.80   $255.80  
  Purchase #4 $58.43   3.823%   $60.6638   $60.66   $60.65   $60.70  
  Purchase #5 $249.75   4.789%   $261.7105   $261.71   $261.70   $261.70  
  Purchase #6 $219.66   11.347%   $244.5848   $244.58   $244.60   $244.60  
  Purchase #7 $107.56   10.518%   $118.8732   $118.87   $118.85   $118.90  
  7 purchase totals = $1,029.15       $1,110.5500   $1,110.53   $1,110.50   $1,110.60