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	$6.78	6.802%	$7.2412	$7.24	$7.25	$7.20
Purchase #2	$160.78	7.175%	$172.316	$172.32	$172.30	$172.30
Purchase #3	$177.83	11.193%	$197.7345	$197.73	$197.75	$197.70
Purchase #4	$77.45	7.837%	$83.5198	$83.52	$83.50	$83.50
Purchase #5	$229.70	12.608%	$258.6606	$258.66	$258.65	$258.70
Purchase #6	$209.52	6.541%	$223.2247	$223.22	$223.20	$223.20
Purchase #7	$122.87	3.819%	$127.5624	$127.56	$127.55	$127.60
7 purchase totals =	$984.93		$1,070.2592	$1,070.25	$1,070.20	$1,070.20