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	$80.61	3.232%	$83.2153	$83.22	$83.20	$83.20
Purchase #2	$79.71	11.442%	$88.8304	$88.83	$88.85	$88.80
Purchase #3	$223.44	3.676%	$231.6537	$231.65	$231.65	$231.70
Purchase #4	$159.35	7.581%	$171.4303	$171.43	$171.45	$171.40
Purchase #5	$145.71	5.529%	$153.7663	$153.77	$153.75	$153.80
Purchase #6	$99.43	5.637%	$105.0349	$105.03	$105.05	$105.00
Purchase #7	$169.33	7.265%	$181.6318	$181.63	$181.65	$181.60
7 purchase totals =	$957.58		$1,015.5627	$1,015.56	$1,015.60	$1,015.50