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 $120.69   11.853%   $134.9954   $135.00   $135.00   $135.00  
  Purchase #2 $205.93   7.393%   $221.1544   $221.15   $221.15   $221.20  
  Purchase #3 $226.86   5.770%   $239.9498   $239.95   $239.95   $239.90  
  Purchase #4 $13.92   7.586%   $14.976   $14.98   $15.00   $15.00  
  Purchase #5 $49.42   13.606%   $56.1441   $56.14   $56.15   $56.10  
  Purchase #6 $56.85   10.381%   $62.7516   $62.75   $62.75   $62.80  
  Purchase #7 $207.69   3.187%   $214.3091   $214.31   $214.30   $214.30  
  7 purchase totals = $881.36       $944.2804   $944.28   $944.30   $944.30