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 $237.89   6.752%   $253.9523   $253.95   $253.95   $254.00  
  Purchase #2 $77.34   4.454%   $80.7847   $80.78   $80.80   $80.80  
  Purchase #3 $53.88   4.309%   $56.2017   $56.20   $56.20   $56.20  
  Purchase #4 $190.42   9.748%   $208.9821   $208.98   $209.00   $209.00  
  Purchase #5 $65.49   6.523%   $69.7619   $69.76   $69.75   $69.80  
  Purchase #6 $201.52   5.347%   $212.2953   $212.30   $212.30   $212.30  
  Purchase #7 $20.73   12.255%   $23.2705   $23.27   $23.25   $23.30  
  7 purchase totals = $847.27       $905.2485   $905.24   $905.25   $905.40