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 $227.97   3.434%   $235.7985   $235.80   $235.80   $235.80  
  Purchase #2 $33.90   3.297%   $35.0177   $35.02   $35.00   $35.00  
  Purchase #3 $237.44   6.234%   $252.242   $252.24   $252.25   $252.20  
  Purchase #4 $231.63   5.401%   $244.1403   $244.14   $244.15   $244.10  
  Purchase #5 $157.34   11.645%   $175.6622   $175.66   $175.65   $175.70  
  Purchase #6 $77.86   6.348%   $82.8026   $82.80   $82.80   $82.80  
  Purchase #7 $160.92   4.163%   $167.6191   $167.62   $167.60   $167.60  
  7 purchase totals = $1,127.06       $1,193.2824   $1,193.28   $1,193.25   $1,193.20