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 $140.67   12.540%   $158.31   $158.31   $158.30   $158.30  
  Purchase #2 $217.80   12.516%   $245.0598   $245.06   $245.05   $245.10  
  Purchase #3 $32.82   7.257%   $35.2017   $35.20   $35.20   $35.20  
  Purchase #4 $14.58   8.154%   $15.7689   $15.77   $15.75   $15.80  
  Purchase #5 $136.38   11.194%   $151.6464   $151.65   $151.65   $151.60  
  Purchase #6 $203.69   5.119%   $214.1169   $214.12   $214.10   $214.10  
  Purchase #7 $56.64   11.303%   $63.042   $63.04   $63.05   $63.00  
  7 purchase totals = $802.58       $883.1457   $883.15   $883.10   $883.10