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	$221.25	11.819%	$247.3995	$247.40	$247.40	$247.40
Purchase #2	$90.99	10.458%	$100.5057	$100.51	$100.50	$100.50
Purchase #3	$28.56	3.398%	$29.5305	$29.53	$29.55	$29.50
Purchase #4	$57.86	13.225%	$65.512	$65.51	$65.50	$65.50
Purchase #5	$105.58	11.450%	$117.6689	$117.67	$117.65	$117.70
Purchase #6	$53.93	4.305%	$56.2517	$56.25	$56.25	$56.30
Purchase #7	$209.89	4.775%	$219.9122	$219.91	$219.90	$219.90
7 purchase totals =	$768.06		$836.7805	$836.78	$836.75	$836.80