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 $175.87   11.801%   $196.6244   $196.62   $196.60   $196.60  
  Purchase #2 $151.71   13.828%   $172.6885   $172.69   $172.70   $172.70  
  Purchase #3 $24.72   8.250%   $26.7594   $26.76   $26.75   $26.80  
  Purchase #4 $72.36   13.423%   $82.0729   $82.07   $82.05   $82.10  
  Purchase #5 $107.80   8.834%   $117.3231   $117.32   $117.30   $117.30  
  Purchase #6 $65.78   12.599%   $74.0676   $74.07   $74.05   $74.10  
  Purchase #7 $58.75   12.600%   $66.1525   $66.15   $66.15   $66.20  
  7 purchase totals = $656.99       $735.6884   $735.68   $735.60   $735.80