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 $55.34   9.519%   $60.6078   $60.61   $60.60   $60.60  
  Purchase #2 $158.40   4.819%   $166.0333   $166.03   $166.05   $166.00  
  Purchase #3 $96.77   3.706%   $100.3563   $100.36   $100.35   $100.40  
  Purchase #4 $240.64   11.147%   $267.4641   $267.46   $267.45   $267.50  
  Purchase #5 $107.54   11.358%   $119.7544   $119.75   $119.75   $119.80  
  Purchase #6 $208.67   8.784%   $226.9996   $227.00   $227.00   $227.00  
  Purchase #7 $216.70   5.517%   $228.6553   $228.66   $228.65   $228.70  
  7 purchase totals = $1,084.06       $1,169.8708   $1,169.87   $1,169.85   $1,170.00