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 $40.73   13.504%   $46.2302   $46.23   $46.25   $46.20  
  Purchase #2 $239.58   11.407%   $266.9089   $266.91   $266.90   $266.90  
  Purchase #3 $216.45   13.516%   $245.7054   $245.71   $245.70   $245.70  
  Purchase #4 $21.51   10.516%   $23.772   $23.77   $23.75   $23.80  
  Purchase #5 $200.62   4.305%   $209.2567   $209.26   $209.25   $209.30  
  Purchase #6 $81.98   4.438%   $85.6183   $85.62   $85.60   $85.60  
  Purchase #7 $149.79   8.224%   $162.1087   $162.11   $162.10   $162.10  
  7 purchase totals = $950.66       $1,039.6002   $1,039.61   $1,039.55   $1,039.60