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 $137.61   13.522%   $156.2176   $156.22   $156.20   $156.20  
  Purchase #2 $247.49   5.561%   $261.2529   $261.25   $261.25   $261.30  
  Purchase #3 $69.37   9.533%   $75.983   $75.98   $76.00   $76.00  
  Purchase #4 $50.88   9.794%   $55.8632   $55.86   $55.85   $55.90  
  Purchase #5 $98.66   5.323%   $103.9117   $103.91   $103.90   $103.90  
  Purchase #6 $202.53   5.379%   $213.4241   $213.42   $213.40   $213.40  
  Purchase #7 $44.58   7.818%   $48.0653   $48.07   $48.05   $48.10  
  7 purchase totals = $851.12       $914.7178   $914.71   $914.65   $914.80