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	$135.78	7.599%	$146.0979	$146.10	$146.10	$146.10
Purchase #2	$91.55	12.197%	$102.7164	$102.72	$102.70	$102.70
Purchase #3	$173.39	10.712%	$191.9635	$191.96	$191.95	$192.00
Purchase #4	$129.51	12.374%	$145.5356	$145.54	$145.55	$145.50
Purchase #5	$69.87	12.585%	$78.6631	$78.66	$78.65	$78.70
Purchase #6	$70.71	3.761%	$73.3694	$73.37	$73.35	$73.40
Purchase #7	$244.47	4.868%	$256.3708	$256.37	$256.35	$256.40
7 purchase totals =	$915.28		$994.7167	$994.72	$994.65	$994.80