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 $248.45   6.791%   $265.3222   $265.32   $265.30   $265.30  
  Purchase #2 $225.49   11.103%   $250.5262   $250.53   $250.55   $250.50  
  Purchase #3 $102.70   5.107%   $107.9449   $107.94   $107.95   $107.90  
  Purchase #4 $97.34   4.318%   $101.5431   $101.54   $101.55   $101.50  
  Purchase #5 $206.51   8.223%   $223.4913   $223.49   $223.50   $223.50  
  Purchase #6 $240.35   3.683%   $249.2021   $249.20   $249.20   $249.20  
  Purchase #7 $239.31   11.354%   $266.4813   $266.48   $266.50   $266.50  
  7 purchase totals = $1,360.15       $1,464.5111   $1,464.50   $1,464.55   $1,464.40