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 $13.48   7.149%   $14.4437   $14.44   $14.45   $14.40  
  Purchase #2 $122.64   5.499%   $129.384   $129.38   $129.40   $129.40  
  Purchase #3 $223.92   12.734%   $252.434   $252.43   $252.45   $252.40  
  Purchase #4 $89.42   5.334%   $94.1897   $94.19   $94.20   $94.20  
  Purchase #5 $42.36   11.623%   $47.2835   $47.28   $47.30   $47.30  
  Purchase #6 $24.40   12.618%   $27.4788   $27.48   $27.50   $27.50  
  Purchase #7 $77.63   4.248%   $80.9277   $80.93   $80.95   $80.90  
  7 purchase totals = $593.85       $646.1414   $646.13   $646.25   $646.10