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	$17.72	4.399%	$18.4995	$18.50	$18.50	$18.50
Purchase #2	$52.97	6.675%	$56.5057	$56.51	$56.50	$56.50
Purchase #3	$71.74	10.685%	$79.4054	$79.41	$79.40	$79.40
Purchase #4	$157.32	6.512%	$167.5647	$167.56	$167.55	$167.60
Purchase #5	$174.65	12.371%	$196.256	$196.26	$196.25	$196.30
Purchase #6	$65.96	4.233%	$68.7521	$68.75	$68.75	$68.80
Purchase #7	$7.89	10.677%	$8.7324	$8.73	$8.75	$8.70
7 purchase totals =	$548.25		$595.7158	$595.72	$595.70	$595.80