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 $112.72   12.695%   $127.0298   $127.03   $127.05   $127.00  
  Purchase #2 $124.38   11.486%   $138.6663   $138.67   $138.65   $138.70  
  Purchase #3 $52.98   4.304%   $55.2603   $55.26   $55.25   $55.30  
  Purchase #4 $153.76   10.523%   $169.9402   $169.94   $169.95   $169.90  
  Purchase #5 $57.73   9.248%   $63.0689   $63.07   $63.05   $63.10  
  Purchase #6 $137.63   13.799%   $156.6216   $156.62   $156.60   $156.60  
  Purchase #7 $219.35   6.530%   $233.6736   $233.67   $233.65   $233.70  
  7 purchase totals = $858.55       $944.2607   $944.26   $944.20   $944.30