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 $48.89   9.526%   $53.5473   $53.55   $53.55   $53.50  
  Purchase #2 $53.38   12.867%   $60.2484   $60.25   $60.25   $60.20  
  Purchase #3 $141.78   11.717%   $158.3924   $158.39   $158.40   $158.40  
  Purchase #4 $61.47   12.365%   $69.0708   $69.07   $69.05   $69.10  
  Purchase #5 $211.62   4.715%   $221.5979   $221.60   $221.60   $221.60  
  Purchase #6 $222.57   6.670%   $237.4154   $237.42   $237.40   $237.40  
  Purchase #7 $212.95   13.766%   $242.2647   $242.26   $242.25   $242.30  
  7 purchase totals = $952.66       $1,042.5369   $1,042.54   $1,042.50   $1,042.50