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 $219.74   13.707%   $249.8598   $249.86   $249.85   $249.90  
  Purchase #2 $233.43   4.871%   $244.8004   $244.80   $244.80   $244.80  
  Purchase #3 $215.83   11.601%   $240.8684   $240.87   $240.85   $240.90  
  Purchase #4 $193.53   6.230%   $205.5869   $205.59   $205.60   $205.60  
  Purchase #5 $177.54   7.702%   $191.2141   $191.21   $191.20   $191.20  
  Purchase #6 $140.87   7.362%   $151.2408   $151.24   $151.25   $151.20  
  Purchase #7 $80.74   4.438%   $84.3232   $84.32   $84.30   $84.30  
  7 purchase totals = $1,261.68       $1,367.8936   $1,367.89   $1,367.85   $1,367.90