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	$73.49	8.160%	$79.4868	$79.49	$79.50	$79.50
Purchase #2	$14.54	7.197%	$15.5864	$15.59	$15.60	$15.60
Purchase #3	$232.29	11.834%	$259.7792	$259.78	$259.80	$259.80
Purchase #4	$239.38	6.354%	$254.5902	$254.59	$254.60	$254.60
Purchase #5	$86.67	3.850%	$90.0068	$90.01	$90.00	$90.00
Purchase #6	$154.28	5.402%	$162.6142	$162.61	$162.60	$162.60
Purchase #7	$136.39	10.259%	$150.3823	$150.38	$150.40	$150.40
7 purchase totals =	$937.04		$1,012.4459	$1,012.45	$1,012.50	$1,012.50