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 $96.39   3.462%   $99.727   $99.73   $99.75   $99.70  
  Purchase #2 $60.67   4.235%   $63.2394   $63.24   $63.25   $63.20  
  Purchase #3 $42.92   8.657%   $46.6356   $46.64   $46.65   $46.60  
  Purchase #4 $211.61   8.513%   $229.6244   $229.62   $229.60   $229.60  
  Purchase #5 $136.42   4.366%   $142.3761   $142.38   $142.40   $142.40  
  Purchase #6 $128.30   3.110%   $132.2901   $132.29   $132.30   $132.30  
  Purchase #7 $49.70   7.852%   $53.6024   $53.60   $53.60   $53.60  
  7 purchase totals = $726.01       $767.4950   $767.50   $767.55   $767.40