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 $47.79   11.518%   $53.2945   $53.29   $53.30   $53.30  
  Purchase #2 $103.83   3.693%   $107.6644   $107.66   $107.65   $107.70  
  Purchase #3 $241.34   8.681%   $262.2907   $262.29   $262.30   $262.30  
  Purchase #4 $95.79   5.779%   $101.3257   $101.33   $101.35   $101.30  
  Purchase #5 $221.66   7.105%   $237.4089   $237.41   $237.40   $237.40  
  Purchase #6 $204.88   3.785%   $212.6347   $212.63   $212.65   $212.60  
  Purchase #7 $54.70   9.440%   $59.8637   $59.86   $59.85   $59.90  
  7 purchase totals = $969.99       $1,034.4826   $1,034.47   $1,034.50   $1,034.50