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 $48.76   4.462%   $50.9357   $50.94   $50.95   $50.90  
  Purchase #2 $105.43   13.857%   $120.0394   $120.04   $120.05   $120.00  
  Purchase #3 $166.36   4.376%   $173.6399   $173.64   $173.65   $173.60  
  Purchase #4 $240.94   12.787%   $271.749   $271.75   $271.75   $271.70  
  Purchase #5 $146.49   5.332%   $154.3008   $154.30   $154.30   $154.30  
  Purchase #6 $183.52   13.423%   $208.1539   $208.15   $208.15   $208.20  
  Purchase #7 $195.48   4.522%   $204.3196   $204.32   $204.30   $204.30  
  7 purchase totals = $1,086.98       $1,183.1383   $1,183.14   $1,183.15   $1,183.00