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 $26.73   10.469%   $29.5284   $29.53   $29.55   $29.50  
  Purchase #2 $58.41   6.760%   $62.3585   $62.36   $62.35   $62.40  
  Purchase #3 $70.94   7.664%   $76.3768   $76.38   $76.40   $76.40  
  Purchase #4 $51.98   13.190%   $58.8362   $58.84   $58.85   $58.80  
  Purchase #5 $43.79   3.227%   $45.2031   $45.20   $45.20   $45.20  
  Purchase #6 $175.60   13.440%   $199.2006   $199.20   $199.20   $199.20  
  Purchase #7 $225.31   7.723%   $242.7107   $242.71   $242.70   $242.70  
  7 purchase totals = $652.76       $714.2143   $714.22   $714.25   $714.20