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 $59.46   4.234%   $61.9775   $61.98   $62.00   $62.00  
  Purchase #2 $16.40   5.247%   $17.2605   $17.26   $17.25   $17.30  
  Purchase #3 $131.72   6.295%   $140.0118   $140.01   $140.00   $140.00  
  Purchase #4 $106.72   11.602%   $119.1017   $119.10   $119.10   $119.10  
  Purchase #5 $74.45   11.368%   $82.9135   $82.91   $82.90   $82.90  
  Purchase #6 $39.29   10.853%   $43.5541   $43.55   $43.55   $43.60  
  Purchase #7 $206.76   8.866%   $225.0913   $225.09   $225.10   $225.10  
  7 purchase totals = $634.80       $689.9104   $689.90   $689.90   $690.00