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 $54.36   11.672%   $60.7049   $60.70   $60.70   $60.70  
  Purchase #2 $223.63   7.614%   $240.6572   $240.66   $240.65   $240.70  
  Purchase #3 $228.36   11.707%   $255.0941   $255.09   $255.10   $255.10  
  Purchase #4 $93.74   11.215%   $104.2529   $104.25   $104.25   $104.30  
  Purchase #5 $47.80   6.771%   $51.0365   $51.04   $51.05   $51.00  
  Purchase #6 $29.42   10.611%   $32.5418   $32.54   $32.55   $32.50  
  Purchase #7 $176.56   4.716%   $184.8866   $184.89   $184.90   $184.90  
  7 purchase totals = $853.87       $929.1740   $929.17   $929.20   $929.20