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	$165.65	6.193%	$175.9087	$175.91	$175.90	$175.90
Purchase #2	$41.81	8.458%	$45.3463	$45.35	$45.35	$45.30
Purchase #3	$140.57	12.119%	$157.6057	$157.61	$157.60	$157.60
Purchase #4	$120.87	6.844%	$129.1423	$129.14	$129.15	$129.10
Purchase #5	$99.27	12.621%	$111.7989	$111.80	$111.80	$111.80
Purchase #6	$139.74	3.673%	$144.8727	$144.87	$144.85	$144.90
Purchase #7	$38.97	8.783%	$42.3927	$42.39	$42.40	$42.40
7 purchase totals =	$746.88		$807.0673	$807.07	$807.05	$807.00