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 $88.86   10.804%   $98.4604   $98.46   $98.45   $98.50  
  Purchase #2 $226.76   9.871%   $249.1435   $249.14   $249.15   $249.10  
  Purchase #3 $59.68   10.586%   $65.9977   $66.00   $66.00   $66.00  
  Purchase #4 $105.79   9.368%   $115.7004   $115.70   $115.70   $115.70  
  Purchase #5 $208.77   13.103%   $236.1251   $236.13   $236.15   $236.10  
  Purchase #6 $204.25   11.517%   $227.7735   $227.77   $227.75   $227.80  
  Purchase #7 $46.99   13.501%   $53.3341   $53.33   $53.35   $53.30  
  7 purchase totals = $941.10       $1,046.5347   $1,046.53   $1,046.55   $1,046.50