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	$141.37	3.766%	$146.694	$146.69	$146.70	$146.70
Purchase #2	$110.30	10.157%	$121.5032	$121.50	$121.50	$121.50
Purchase #3	$25.32	13.758%	$28.8035	$28.80	$28.80	$28.80
Purchase #4	$38.28	10.663%	$42.3618	$42.36	$42.35	$42.40
Purchase #5	$57.74	6.196%	$61.3176	$61.32	$61.30	$61.30
Purchase #6	$247.45	13.874%	$281.7812	$281.78	$281.80	$281.80
Purchase #7	$57.92	13.463%	$65.7178	$65.72	$65.70	$65.70
7 purchase totals =	$678.38		$748.1791	$748.17	$748.15	$748.20