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 $214.25   3.471%   $221.6866   $221.69   $221.70   $221.70  
  Purchase #2 $68.47   6.837%   $73.1513   $73.15   $73.15   $73.20  
  Purchase #3 $69.96   11.551%   $78.0411   $78.04   $78.05   $78.00  
  Purchase #4 $22.43   11.584%   $25.0283   $25.03   $25.05   $25.00  
  Purchase #5 $51.95   9.561%   $56.9169   $56.92   $56.90   $56.90  
  Purchase #6 $13.43   11.727%   $15.0049   $15.00   $15.00   $15.00  
  Purchase #7 $155.52   3.657%   $161.2074   $161.21   $161.20   $161.20  
  7 purchase totals = $596.01       $631.0365   $631.04   $631.05   $631.00