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 $212.71   3.401%   $219.9443   $219.94   $219.95   $219.90  
  Purchase #2 $85.71   11.868%   $95.8821   $95.88   $95.90   $95.90  
  Purchase #3 $132.39   9.290%   $144.689   $144.69   $144.70   $144.70  
  Purchase #4 $32.26   13.404%   $36.5841   $36.58   $36.60   $36.60  
  Purchase #5 $221.83   6.747%   $236.7969   $236.80   $236.80   $236.80  
  Purchase #6 $237.99   5.289%   $250.5773   $250.58   $250.60   $250.60  
  Purchase #7 $52.96   11.335%   $58.963   $58.96   $58.95   $59.00  
  7 purchase totals = $975.85       $1,043.4367   $1,043.43   $1,043.50   $1,043.50