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	$68.90	5.696%	$72.8245	$72.82	$72.80	$72.80
Purchase #2	$184.60	7.762%	$198.9287	$198.93	$198.95	$198.90
Purchase #3	$98.32	13.647%	$111.7377	$111.74	$111.75	$111.70
Purchase #4	$146.50	10.447%	$161.8049	$161.80	$161.80	$161.80
Purchase #5	$37.88	11.183%	$42.1161	$42.12	$42.10	$42.10
Purchase #6	$78.51	6.527%	$83.6343	$83.63	$83.65	$83.60
Purchase #7	$138.26	11.859%	$154.6563	$154.66	$154.65	$154.70
7 purchase totals =	$752.97		$825.7025	$825.70	$825.70	$825.60