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 $61.47   11.264%   $68.394   $68.39   $68.40   $68.40  
  Purchase #2 $33.83   7.863%   $36.4901   $36.49   $36.50   $36.50  
  Purchase #3 $47.94   6.421%   $51.0182   $51.02   $51.00   $51.00  
  Purchase #4 $244.53   9.767%   $268.4132   $268.41   $268.40   $268.40  
  Purchase #5 $101.66   9.273%   $111.0869   $111.09   $111.10   $111.10  
  Purchase #6 $199.60   4.833%   $209.2467   $209.25   $209.25   $209.20  
  Purchase #7 $154.93   13.762%   $176.2515   $176.25   $176.25   $176.30  
  7 purchase totals = $843.96       $920.9006   $920.90   $920.90   $920.90