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 $119.34   6.411%   $126.9909   $126.99   $127.00   $127.00  
  Purchase #2 $13.31   7.393%   $14.294   $14.29   $14.30   $14.30  
  Purchase #3 $21.73   7.568%   $23.3745   $23.37   $23.35   $23.40  
  Purchase #4 $37.31   13.808%   $42.4618   $42.46   $42.45   $42.50  
  Purchase #5 $225.99   10.154%   $248.937   $248.94   $248.95   $248.90  
  Purchase #6 $210.58   10.869%   $233.4679   $233.47   $233.45   $233.50  
  Purchase #7 $97.46   9.426%   $106.6466   $106.65   $106.65   $106.60  
  7 purchase totals = $725.72       $796.1727   $796.17   $796.15   $796.20