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 $55.96   9.329%   $61.1805   $61.18   $61.20   $61.20  
  Purchase #2 $48.54   10.861%   $53.8119   $53.81   $53.80   $53.80  
  Purchase #3 $224.26   12.451%   $252.1826   $252.18   $252.20   $252.20  
  Purchase #4 $66.65   8.481%   $72.3026   $72.30   $72.30   $72.30  
  Purchase #5 $117.51   4.788%   $123.1364   $123.14   $123.15   $123.10  
  Purchase #6 $117.45   13.199%   $132.9522   $132.95   $132.95   $133.00  
  Purchase #7 $206.29   8.648%   $224.13   $224.13   $224.15   $224.10  
  7 purchase totals = $836.66       $919.6962   $919.69   $919.75   $919.70