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 $84.69   9.713%   $92.9159   $92.92   $92.90   $92.90  
  Purchase #2 $175.80   12.420%   $197.6344   $197.63   $197.65   $197.60  
  Purchase #3 $239.86   3.823%   $249.0298   $249.03   $249.05   $249.00  
  Purchase #4 $116.85   13.772%   $132.9426   $132.94   $132.95   $132.90  
  Purchase #5 $201.69   12.599%   $227.1009   $227.10   $227.10   $227.10  
  Purchase #6 $234.62   10.446%   $259.1284   $259.13   $259.15   $259.10  
  Purchase #7 $140.58   4.315%   $146.646   $146.65   $146.65   $146.60  
  7 purchase totals = $1,194.09       $1,305.3980   $1,305.40   $1,305.45   $1,305.20