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 $116.42   11.778%   $130.1319   $130.13   $130.15   $130.10  
  Purchase #2 $245.53   13.777%   $279.3567   $279.36   $279.35   $279.40  
  Purchase #3 $14.25   5.722%   $15.0654   $15.07   $15.05   $15.10  
  Purchase #4 $248.95   6.653%   $265.5126   $265.51   $265.50   $265.50  
  Purchase #5 $159.87   11.246%   $177.849   $177.85   $177.85   $177.80  
  Purchase #6 $157.30   8.345%   $170.4267   $170.43   $170.45   $170.40  
  Purchase #7 $167.73   11.817%   $187.5507   $187.55   $187.55   $187.60  
  7 purchase totals = $1,110.05       $1,225.8930   $1,225.90   $1,225.90   $1,225.90