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 $209.83   8.408%   $227.4725   $227.47   $227.45   $227.50  
  Purchase #2 $72.95   3.189%   $75.2764   $75.28   $75.30   $75.30  
  Purchase #3 $121.87   12.336%   $136.9039   $136.90   $136.90   $136.90  
  Purchase #4 $56.27   5.267%   $59.2337   $59.23   $59.25   $59.20  
  Purchase #5 $69.40   3.261%   $71.6631   $71.66   $71.65   $71.70  
  Purchase #6 $59.27   4.589%   $61.9899   $61.99   $62.00   $62.00  
  Purchase #7 $62.92   11.416%   $70.1029   $70.10   $70.10   $70.10  
  7 purchase totals = $652.51       $702.6424   $702.63   $702.65   $702.70