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	$97.74	8.488%	$106.0362	$106.04	$106.05	$106.00
Purchase #2	$225.77	13.400%	$256.0232	$256.02	$256.00	$256.00
Purchase #3	$210.33	13.466%	$238.653	$238.65	$238.65	$238.70
Purchase #4	$127.34	5.585%	$134.4519	$134.45	$134.45	$134.50
Purchase #5	$115.37	6.815%	$123.2325	$123.23	$123.25	$123.20
Purchase #6	$172.81	4.143%	$179.9695	$179.97	$179.95	$180.00
Purchase #7	$89.89	10.699%	$99.5073	$99.51	$99.50	$99.50
7 purchase totals =	$1,039.25		$1,137.8736	$1,137.87	$1,137.85	$1,137.90