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 $41.89   11.232%   $46.5951   $46.60   $46.60   $46.60  
  Purchase #2 $185.35   12.522%   $208.5595   $208.56   $208.55   $208.60  
  Purchase #3 $151.62   4.633%   $158.6446   $158.64   $158.65   $158.60  
  Purchase #4 $227.81   9.867%   $250.288   $250.29   $250.30   $250.30  
  Purchase #5 $12.55   11.377%   $13.9778   $13.98   $14.00   $14.00  
  Purchase #6 $22.63   10.719%   $25.0557   $25.06   $25.05   $25.10  
  Purchase #7 $77.66   4.346%   $81.0351   $81.04   $81.05   $81.00  
  7 purchase totals = $719.51       $784.1558   $784.17   $784.20   $784.20