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	$26.72	3.503%	$27.656	$27.66	$27.65	$27.70
Purchase #2	$139.27	10.700%	$154.1719	$154.17	$154.15	$154.20
Purchase #3	$127.40	13.718%	$144.8767	$144.88	$144.90	$144.90
Purchase #4	$135.72	8.203%	$146.8531	$146.85	$146.85	$146.90
Purchase #5	$213.54	13.281%	$241.9002	$241.90	$241.90	$241.90
Purchase #6	$49.76	3.312%	$51.4081	$51.41	$51.40	$51.40
Purchase #7	$53.83	11.592%	$60.07	$60.07	$60.05	$60.10
7 purchase totals =	$746.24		$826.9360	$826.94	$826.90	$827.10