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 $91.83   13.543%   $104.2665   $104.27   $104.25   $104.30  
  Purchase #2 $167.89   11.219%   $186.7256   $186.73   $186.75   $186.70  
  Purchase #3 $78.26   10.420%   $86.4147   $86.41   $86.40   $86.40  
  Purchase #4 $184.79   5.118%   $194.2476   $194.25   $194.25   $194.20  
  Purchase #5 $204.42   4.293%   $213.1958   $213.20   $213.20   $213.20  
  Purchase #6 $190.55   7.783%   $205.3805   $205.38   $205.40   $205.40  
  Purchase #7 $206.42   9.567%   $226.1682   $226.17   $226.15   $226.20  
  7 purchase totals = $1,124.16       $1,216.3989   $1,216.41   $1,216.40   $1,216.40