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 $57.98   3.687%   $60.1177   $60.12   $60.10   $60.10  
  Purchase #2 $220.68   8.702%   $239.8836   $239.88   $239.90   $239.90  
  Purchase #3 $156.79   8.202%   $169.6499   $169.65   $169.65   $169.60  
  Purchase #4 $60.68   7.436%   $65.1922   $65.19   $65.20   $65.20  
  Purchase #5 $32.46   11.763%   $36.2783   $36.28   $36.30   $36.30  
  Purchase #6 $35.26   9.864%   $38.738   $38.74   $38.75   $38.70  
  Purchase #7 $199.66   12.338%   $224.2941   $224.29   $224.30   $224.30  
  7 purchase totals = $763.51       $834.1538   $834.15   $834.20   $834.10