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 $82.59   13.791%   $93.98   $93.98   $94.00   $94.00  
  Purchase #2 $103.99   8.306%   $112.6274   $112.63   $112.65   $112.60  
  Purchase #3 $82.77   7.205%   $88.7336   $88.73   $88.75   $88.70  
  Purchase #4 $74.71   10.162%   $82.302   $82.30   $82.30   $82.30  
  Purchase #5 $110.91   5.565%   $117.0821   $117.08   $117.10   $117.10  
  Purchase #6 $161.51   11.383%   $179.8947   $179.89   $179.90   $179.90  
  Purchase #7 $217.34   3.823%   $225.6489   $225.65   $225.65   $225.60  
  7 purchase totals = $833.82       $900.2687   $900.26   $900.35   $900.20