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	$143.64	3.382%	$148.4979	$148.50	$148.50	$148.50
Purchase #2	$227.43	13.618%	$258.4014	$258.40	$258.40	$258.40
Purchase #3	$60.46	8.194%	$65.4141	$65.41	$65.40	$65.40
Purchase #4	$203.65	12.404%	$228.9107	$228.91	$228.90	$228.90
Purchase #5	$186.95	12.554%	$210.4197	$210.42	$210.40	$210.40
Purchase #6	$90.33	11.428%	$100.6529	$100.65	$100.65	$100.70
Purchase #7	$146.76	6.215%	$155.8811	$155.88	$155.90	$155.90
7 purchase totals =	$1,059.22		$1,168.1778	$1,168.17	$1,168.15	$1,168.20