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 $106.41   11.104%   $118.2258   $118.23   $118.25   $118.20  
  Purchase #2 $171.43   8.857%   $186.6136   $186.61   $186.60   $186.60  
  Purchase #3 $144.67   5.246%   $152.2594   $152.26   $152.25   $152.30  
  Purchase #4 $18.73   5.339%   $19.73   $19.73   $19.75   $19.70  
  Purchase #5 $171.28   9.749%   $187.9781   $187.98   $188.00   $188.00  
  Purchase #6 $194.87   3.529%   $201.747   $201.75   $201.75   $201.70  
  Purchase #7 $44.46   7.676%   $47.8727   $47.87   $47.85   $47.90  
  7 purchase totals = $851.85       $914.4266   $914.43   $914.45   $914.40