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 $226.99   3.316%   $234.517   $234.52   $234.50   $234.50  
  Purchase #2 $182.34   9.602%   $199.8483   $199.85   $199.85   $199.80  
  Purchase #3 $244.41   13.680%   $277.8453   $277.85   $277.85   $277.80  
  Purchase #4 $161.42   13.794%   $183.6863   $183.69   $183.70   $183.70  
  Purchase #5 $146.43   13.505%   $166.2054   $166.21   $166.20   $166.20  
  Purchase #6 $33.98   5.541%   $35.8628   $35.86   $35.85   $35.90  
  Purchase #7 $118.52   6.345%   $126.0401   $126.04   $126.05   $126.00  
  7 purchase totals = $1,114.09       $1,224.0052   $1,224.02   $1,224.00   $1,223.90