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 $91.79   6.712%   $97.9509   $97.95   $97.95   $98.00  
  Purchase #2 $156.44   9.242%   $170.8982   $170.90   $170.90   $170.90  
  Purchase #3 $66.63   3.331%   $68.8494   $68.85   $68.85   $68.80  
  Purchase #4 $192.56   7.372%   $206.7555   $206.76   $206.75   $206.80  
  Purchase #5 $13.71   3.786%   $14.2291   $14.23   $14.25   $14.20  
  Purchase #6 $49.82   6.201%   $52.9093   $52.91   $52.90   $52.90  
  Purchase #7 $57.71   5.617%   $60.9516   $60.95   $60.95   $61.00  
  7 purchase totals = $628.66       $672.5440   $672.55   $672.55   $672.60