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 $60.53   8.703%   $65.7979   $65.80   $65.80   $65.80  
  Purchase #2 $214.47   6.193%   $227.7521   $227.75   $227.75   $227.80  
  Purchase #3 $226.34   8.762%   $246.1719   $246.17   $246.15   $246.20  
  Purchase #4 $245.96   7.249%   $263.7896   $263.79   $263.80   $263.80  
  Purchase #5 $209.83   10.116%   $231.0564   $231.06   $231.05   $231.10  
  Purchase #6 $230.47   11.190%   $256.2596   $256.26   $256.25   $256.30  
  Purchase #7 $220.58   8.697%   $239.7638   $239.76   $239.75   $239.80  
  7 purchase totals = $1,408.18       $1,530.5913   $1,530.59   $1,530.55   $1,530.80