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	$153.73	11.375%	$171.2168	$171.22	$171.20	$171.20
Purchase #2	$43.49	13.634%	$49.4194	$49.42	$49.40	$49.40
Purchase #3	$211.90	10.232%	$233.5816	$233.58	$233.60	$233.60
Purchase #4	$161.47	6.821%	$172.4839	$172.48	$172.50	$172.50
Purchase #5	$72.51	11.209%	$80.6376	$80.64	$80.65	$80.60
Purchase #6	$12.48	3.277%	$12.889	$12.89	$12.90	$12.90
Purchase #7	$93.69	5.133%	$98.4991	$98.50	$98.50	$98.50
7 purchase totals =	$749.27		$818.7274	$818.73	$818.75	$818.70