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 $57.98   13.706%   $65.9267   $65.93   $65.95   $65.90  
  Purchase #2 $146.97   6.486%   $156.5025   $156.50   $156.50   $156.50  
  Purchase #3 $111.25   11.813%   $124.392   $124.39   $124.40   $124.40  
  Purchase #4 $48.73   7.616%   $52.4413   $52.44   $52.45   $52.40  
  Purchase #5 $164.71   11.117%   $183.0208   $183.02   $183.00   $183.00  
  Purchase #6 $205.46   10.581%   $227.1997   $227.20   $227.20   $227.20  
  Purchase #7 $67.51   11.313%   $75.1474   $75.15   $75.15   $75.10  
  7 purchase totals = $802.61       $884.6304   $884.63   $884.65   $884.50