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 $46.28   4.357%   $48.2964   $48.30   $48.30   $48.30  
  Purchase #2 $62.95   13.865%   $71.678   $71.68   $71.70   $71.70  
  Purchase #3 $153.45   7.263%   $164.5951   $164.60   $164.60   $164.60  
  Purchase #4 $238.66   4.401%   $249.1634   $249.16   $249.15   $249.20  
  Purchase #5 $43.67   10.551%   $48.2776   $48.28   $48.30   $48.30  
  Purchase #6 $198.45   5.251%   $208.8706   $208.87   $208.85   $208.90  
  Purchase #7 $140.74   6.613%   $150.0471   $150.05   $150.05   $150.00  
  7 purchase totals = $884.20       $940.9282   $940.94   $940.95   $941.00