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	$37.39	3.160%	$38.5715	$38.57	$38.55	$38.60
Purchase #2	$40.64	4.743%	$42.5676	$42.57	$42.55	$42.60
Purchase #3	$234.98	13.808%	$267.426	$267.43	$267.45	$267.40
Purchase #4	$135.76	11.810%	$151.7933	$151.79	$151.80	$151.80
Purchase #5	$13.68	8.129%	$14.792	$14.79	$14.80	$14.80
Purchase #6	$243.39	3.501%	$251.9111	$251.91	$251.90	$251.90
Purchase #7	$15.88	10.121%	$17.4872	$17.49	$17.50	$17.50
7 purchase totals =	$721.72		$784.5487	$784.55	$784.55	$784.60