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 $24.63   6.179%   $26.1519   $26.15   $26.15   $26.20  
  Purchase #2 $86.75   11.610%   $96.8217   $96.82   $96.80   $96.80  
  Purchase #3 $30.48   11.533%   $33.9953   $34.00   $34.00   $34.00  
  Purchase #4 $127.42   10.784%   $141.161   $141.16   $141.15   $141.20  
  Purchase #5 $171.95   8.465%   $186.5056   $186.51   $186.50   $186.50  
  Purchase #6 $13.70   6.488%   $14.5889   $14.59   $14.60   $14.60  
  Purchase #7 $209.36   11.632%   $233.7128   $233.71   $233.70   $233.70  
  7 purchase totals = $664.29       $732.9372   $732.94   $732.90   $733.00