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	$238.86	4.873%	$250.4996	$250.50	$250.50	$250.50
Purchase #2	$211.88	8.281%	$229.4258	$229.43	$229.45	$229.40
Purchase #3	$50.80	7.589%	$54.6552	$54.66	$54.65	$54.70
Purchase #4	$148.70	11.536%	$165.854	$165.85	$165.85	$165.90
Purchase #5	$120.33	3.688%	$124.7678	$124.77	$124.75	$124.80
Purchase #6	$140.36	12.209%	$157.4966	$157.50	$157.50	$157.50
Purchase #7	$173.94	6.435%	$185.133	$185.13	$185.15	$185.10
7 purchase totals =	$1,084.87		$1,167.8320	$1,167.84	$1,167.85	$1,167.90