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 $40.90   8.226%   $44.2644   $44.26   $44.25   $44.30  
  Purchase #2 $215.49   6.565%   $229.6369   $229.64   $229.65   $229.60  
  Purchase #3 $36.56   10.182%   $40.2825   $40.28   $40.30   $40.30  
  Purchase #4 $87.45   6.776%   $93.3756   $93.38   $93.40   $93.40  
  Purchase #5 $238.85   12.476%   $268.6489   $268.65   $268.65   $268.60  
  Purchase #6 $9.68   13.483%   $10.9852   $10.99   $11.00   $11.00  
  Purchase #7 $50.55   13.291%   $57.2686   $57.27   $57.25   $57.30  
  7 purchase totals = $679.48       $744.4621   $744.47   $744.50   $744.50