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	$239.41	4.832%	$250.9783	$250.98	$251.00	$251.00
Purchase #2	$88.82	11.820%	$99.3185	$99.32	$99.30	$99.30
Purchase #3	$80.44	3.393%	$83.1693	$83.17	$83.15	$83.20
Purchase #4	$55.58	8.356%	$60.2243	$60.22	$60.20	$60.20
Purchase #5	$28.73	13.666%	$32.6562	$32.66	$32.65	$32.70
Purchase #6	$86.57	4.510%	$90.4743	$90.47	$90.45	$90.50
Purchase #7	$25.97	5.164%	$27.3111	$27.31	$27.30	$27.30
7 purchase totals =	$605.52		$644.1320	$644.13	$644.05	$644.20