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 $164.37   12.469%   $184.8653   $184.87   $184.85   $184.90  
  Purchase #2 $192.38   7.463%   $206.7373   $206.74   $206.75   $206.70  
  Purchase #3 $35.46   3.327%   $36.6398   $36.64   $36.65   $36.60  
  Purchase #4 $128.86   5.760%   $136.2823   $136.28   $136.30   $136.30  
  Purchase #5 $48.71   12.827%   $54.958   $54.96   $54.95   $55.00  
  Purchase #6 $207.96   3.443%   $215.1201   $215.12   $215.10   $215.10  
  Purchase #7 $155.28   9.226%   $169.6061   $169.61   $169.60   $169.60  
  7 purchase totals = $933.02       $1,004.2089   $1,004.22   $1,004.20   $1,004.20