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 $53.73   6.835%   $57.4024   $57.40   $57.40   $57.40  
  Purchase #2 $93.63   10.867%   $103.8048   $103.80   $103.80   $103.80  
  Purchase #3 $86.72   13.341%   $98.2893   $98.29   $98.30   $98.30  
  Purchase #4 $69.44   5.270%   $73.0995   $73.10   $73.10   $73.10  
  Purchase #5 $222.99   11.326%   $248.2458   $248.25   $248.25   $248.20  
  Purchase #6 $193.72   6.294%   $205.9127   $205.91   $205.90   $205.90  
  Purchase #7 $239.32   11.618%   $267.1242   $267.12   $267.10   $267.10  
  7 purchase totals = $959.55       $1,053.8787   $1,053.87   $1,053.85   $1,053.80