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	$134.39	6.643%	$143.3175	$143.32	$143.30	$143.30
Purchase #2	$157.81	9.520%	$172.8335	$172.83	$172.85	$172.80
Purchase #3	$50.55	8.470%	$54.8316	$54.83	$54.85	$54.80
Purchase #4	$127.28	10.456%	$140.5884	$140.59	$140.60	$140.60
Purchase #5	$249.41	10.614%	$275.8824	$275.88	$275.90	$275.90
Purchase #6	$197.73	12.399%	$222.2465	$222.25	$222.25	$222.20
Purchase #7	$197.66	7.720%	$212.9194	$212.92	$212.90	$212.90
7 purchase totals =	$1,114.83		$1,222.6193	$1,222.62	$1,222.65	$1,222.50