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 $53.95   13.140%   $61.039   $61.04   $61.05   $61.00  
  Purchase #2 $91.26   12.725%   $102.8728   $102.87   $102.85   $102.90  
  Purchase #3 $20.57   11.575%   $22.951   $22.95   $22.95   $23.00  
  Purchase #4 $200.69   10.254%   $221.2688   $221.27   $221.25   $221.30  
  Purchase #5 $148.65   6.235%   $157.9183   $157.92   $157.90   $157.90  
  Purchase #6 $46.54   7.234%   $49.9067   $49.91   $49.90   $49.90  
  Purchase #7 $145.95   8.520%   $158.3849   $158.38   $158.40   $158.40  
  7 purchase totals = $707.61       $774.3415   $774.34   $774.30   $774.40