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 $92.84   5.853%   $98.2739   $98.27   $98.25   $98.30  
  Purchase #2 $142.85   4.757%   $149.6454   $149.65   $149.65   $149.60  
  Purchase #3 $57.77   10.296%   $63.718   $63.72   $63.70   $63.70  
  Purchase #4 $25.81   13.825%   $29.3782   $29.38   $29.40   $29.40  
  Purchase #5 $183.26   6.827%   $195.7712   $195.77   $195.75   $195.80  
  Purchase #6 $73.62   9.693%   $80.756   $80.76   $80.75   $80.80  
  Purchase #7 $5.58   13.858%   $6.3533   $6.35   $6.35   $6.40  
  7 purchase totals = $581.73       $623.8960   $623.90   $623.85   $624.00