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 $86.30   11.187%   $95.9544   $95.95   $95.95   $96.00  
  Purchase #2 $6.38   12.361%   $7.1686   $7.17   $7.15   $7.20  
  Purchase #3 $88.27   7.139%   $94.5716   $94.57   $94.55   $94.60  
  Purchase #4 $160.95   8.549%   $174.7096   $174.71   $174.70   $174.70  
  Purchase #5 $118.77   6.564%   $126.5661   $126.57   $126.55   $126.60  
  Purchase #6 $50.60   4.241%   $52.7459   $52.75   $52.75   $52.70  
  Purchase #7 $233.37   12.426%   $262.3686   $262.37   $262.35   $262.40  
  7 purchase totals = $744.64       $814.0848   $814.09   $814.00   $814.20