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 $174.95   10.802%   $193.8481   $193.85   $193.85   $193.80  
  Purchase #2 $112.63   4.179%   $117.3368   $117.34   $117.35   $117.30  
  Purchase #3 $245.42   8.457%   $266.1752   $266.18   $266.20   $266.20  
  Purchase #4 $69.31   5.553%   $73.1588   $73.16   $73.15   $73.20  
  Purchase #5 $83.43   9.571%   $91.4151   $91.42   $91.40   $91.40  
  Purchase #6 $26.60   7.614%   $28.6253   $28.63   $28.65   $28.60  
  Purchase #7 $72.51   5.207%   $76.2856   $76.29   $76.30   $76.30  
  7 purchase totals = $784.85       $846.8449   $846.87   $846.90   $846.80