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 $204.95   9.419%   $224.2542   $224.25   $224.25   $224.30  
  Purchase #2 $36.47   4.497%   $38.1101   $38.11   $38.10   $38.10  
  Purchase #3 $102.63   3.294%   $106.0106   $106.01   $106.00   $106.00  
  Purchase #4 $63.78   9.366%   $69.7536   $69.75   $69.75   $69.80  
  Purchase #5 $185.82   8.322%   $201.2839   $201.28   $201.30   $201.30  
  Purchase #6 $33.61   9.306%   $36.7377   $36.74   $36.75   $36.70  
  Purchase #7 $204.28   5.625%   $215.7708   $215.77   $215.75   $215.80  
  7 purchase totals = $831.54       $891.9209   $891.91   $891.90   $892.00