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 $42.61   12.787%   $48.0585   $48.06   $48.05   $48.10  
  Purchase #2 $106.37   9.652%   $116.6368   $116.64   $116.65   $116.60  
  Purchase #3 $6.26   3.383%   $6.4718   $6.47   $6.45   $6.50  
  Purchase #4 $62.53   3.872%   $64.9512   $64.95   $64.95   $65.00  
  Purchase #5 $161.67   6.105%   $171.54   $171.54   $171.55   $171.50  
  Purchase #6 $218.59   7.239%   $234.4137   $234.41   $234.40   $234.40  
  Purchase #7 $146.37   4.681%   $153.2216   $153.22   $153.20   $153.20  
  7 purchase totals = $744.40       $795.2936   $795.29   $795.25   $795.30