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 $234.94   13.665%   $267.0446   $267.04   $267.05   $267.00  
  Purchase #2 $169.84   8.354%   $184.0284   $184.03   $184.05   $184.00  
  Purchase #3 $197.76   4.796%   $207.2446   $207.24   $207.25   $207.20  
  Purchase #4 $214.59   12.788%   $242.0318   $242.03   $242.05   $242.00  
  Purchase #5 $35.71   10.380%   $39.4167   $39.42   $39.40   $39.40  
  Purchase #6 $150.96   8.189%   $163.3221   $163.32   $163.30   $163.30  
  Purchase #7 $192.98   10.505%   $213.2525   $213.25   $213.25   $213.30  
  7 purchase totals = $1,196.78       $1,316.3407   $1,316.33   $1,316.35   $1,316.20