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 $196.27   12.409%   $220.6251   $220.63   $220.65   $220.60  
  Purchase #2 $98.42   6.209%   $104.5309   $104.53   $104.55   $104.50  
  Purchase #3 $55.92   12.252%   $62.7713   $62.77   $62.75   $62.80  
  Purchase #4 $86.57   10.236%   $95.4313   $95.43   $95.45   $95.40  
  Purchase #5 $75.66   11.825%   $84.6068   $84.61   $84.60   $84.60  
  Purchase #6 $204.57   11.400%   $227.891   $227.89   $227.90   $227.90  
  Purchase #7 $162.69   5.348%   $171.3907   $171.39   $171.40   $171.40  
  7 purchase totals = $880.10       $967.2471   $967.25   $967.30   $967.20