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 $250.95   4.788%   $262.9655   $262.97   $262.95   $263.00  
  Purchase #2 $142.76   12.329%   $160.3609   $160.36   $160.35   $160.40  
  Purchase #3 $56.97   13.128%   $64.449   $64.45   $64.45   $64.40  
  Purchase #4 $43.49   7.189%   $46.6165   $46.62   $46.60   $46.60  
  Purchase #5 $80.61   4.538%   $84.2681   $84.27   $84.25   $84.30  
  Purchase #6 $99.43   10.659%   $110.0282   $110.03   $110.05   $110.00  
  Purchase #7 $42.45   5.178%   $44.6481   $44.65   $44.65   $44.60  
  7 purchase totals = $716.66       $773.3363   $773.35   $773.30   $773.30