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	$91.35	8.480%	$99.0965	$99.10	$99.10	$99.10
Purchase #2	$238.83	12.666%	$269.0802	$269.08	$269.10	$269.10
Purchase #3	$49.27	3.316%	$50.9038	$50.90	$50.90	$50.90
Purchase #4	$134.75	8.665%	$146.4261	$146.43	$146.45	$146.40
Purchase #5	$222.83	6.728%	$237.822	$237.82	$237.80	$237.80
Purchase #6	$202.71	10.428%	$223.8486	$223.85	$223.85	$223.80
Purchase #7	$205.28	6.316%	$218.2455	$218.25	$218.25	$218.20
7 purchase totals =	$1,145.02		$1,245.4227	$1,245.43	$1,245.45	$1,245.30