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 $239.49   9.663%   $262.6319   $262.63   $262.65   $262.60  
  Purchase #2 $183.41   9.188%   $200.2617   $200.26   $200.25   $200.30  
  Purchase #3 $92.88   10.522%   $102.6528   $102.65   $102.65   $102.70  
  Purchase #4 $190.29   5.195%   $200.1756   $200.18   $200.20   $200.20  
  Purchase #5 $72.98   4.505%   $76.2677   $76.27   $76.25   $76.30  
  Purchase #6 $178.69   12.270%   $200.6153   $200.62   $200.60   $200.60  
  Purchase #7 $109.95   7.297%   $117.9731   $117.97   $117.95   $118.00  
  7 purchase totals = $1,067.69       $1,160.5781   $1,160.58   $1,160.55   $1,160.70