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 $217.57   10.763%   $240.9871   $240.99   $241.00   $241.00  
  Purchase #2 $76.87   8.258%   $83.2179   $83.22   $83.20   $83.20  
  Purchase #3 $54.60   4.607%   $57.1154   $57.12   $57.10   $57.10  
  Purchase #4 $225.93   5.728%   $238.8713   $238.87   $238.85   $238.90  
  Purchase #5 $63.77   5.141%   $67.0484   $67.05   $67.05   $67.00  
  Purchase #6 $197.34   6.361%   $209.8928   $209.89   $209.90   $209.90  
  Purchase #7 $220.94   8.236%   $239.1366   $239.14   $239.15   $239.10  
  7 purchase totals = $1,057.02       $1,136.2695   $1,136.28   $1,136.25   $1,136.20