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 $94.73   9.198%   $103.4433   $103.44   $103.45   $103.40  
  Purchase #2 $179.64   13.540%   $203.9633   $203.96   $203.95   $204.00  
  Purchase #3 $247.38   10.203%   $272.6202   $272.62   $272.60   $272.60  
  Purchase #4 $171.79   8.798%   $186.9041   $186.90   $186.90   $186.90  
  Purchase #5 $224.76   10.482%   $248.3193   $248.32   $248.30   $248.30  
  Purchase #6 $41.95   12.561%   $47.2193   $47.22   $47.20   $47.20  
  Purchase #7 $139.26   11.109%   $154.7304   $154.73   $154.75   $154.70  
  7 purchase totals = $1,099.51       $1,217.1999   $1,217.19   $1,217.15   $1,217.10