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	$44.83	13.560%	$50.9089	$50.91	$50.90	$50.90
Purchase #2	$54.99	11.844%	$61.503	$61.50	$61.50	$61.50
Purchase #3	$230.80	12.284%	$259.1515	$259.15	$259.15	$259.20
Purchase #4	$131.27	9.574%	$143.8378	$143.84	$143.85	$143.80
Purchase #5	$102.51	4.177%	$106.7918	$106.79	$106.80	$106.80
Purchase #6	$10.61	4.187%	$11.0542	$11.05	$11.05	$11.10
Purchase #7	$165.87	3.152%	$171.0982	$171.10	$171.10	$171.10
7 purchase totals =	$740.88		$804.3454	$804.34	$804.35	$804.40