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	$242.37	13.730%	$275.6474	$275.65	$275.65	$275.60
Purchase #2	$185.84	7.685%	$200.1218	$200.12	$200.10	$200.10
Purchase #3	$80.65	3.602%	$83.555	$83.56	$83.55	$83.60
Purchase #4	$58.87	3.857%	$61.1406	$61.14	$61.15	$61.10
Purchase #5	$119.82	11.162%	$133.1943	$133.19	$133.20	$133.20
Purchase #6	$219.63	7.678%	$236.4932	$236.49	$236.50	$236.50
Purchase #7	$78.78	6.275%	$83.7234	$83.72	$83.70	$83.70
7 purchase totals =	$985.96		$1,073.8757	$1,073.87	$1,073.85	$1,073.80