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 $48.35   11.746%   $54.0292   $54.03   $54.05   $54.00  
  Purchase #2 $118.69   8.354%   $128.6054   $128.61   $128.60   $128.60  
  Purchase #3 $103.61   11.468%   $115.492   $115.49   $115.50   $115.50  
  Purchase #4 $231.70   7.650%   $249.4251   $249.43   $249.45   $249.40  
  Purchase #5 $114.25   6.676%   $121.8773   $121.88   $121.90   $121.90  
  Purchase #6 $222.43   12.518%   $250.2738   $250.27   $250.25   $250.30  
  Purchase #7 $163.65   12.478%   $184.0702   $184.07   $184.05   $184.10  
  7 purchase totals = $1,002.68       $1,103.7730   $1,103.78   $1,103.80   $1,103.80