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	$74.28	6.220%	$78.9002	$78.90	$78.90	$78.90
Purchase #2	$203.49	11.299%	$226.4823	$226.48	$226.50	$226.50
Purchase #3	$127.90	12.447%	$143.8197	$143.82	$143.80	$143.80
Purchase #4	$42.77	4.182%	$44.5586	$44.56	$44.55	$44.60
Purchase #5	$80.70	13.697%	$91.7535	$91.75	$91.75	$91.80
Purchase #6	$49.67	6.339%	$52.8186	$52.82	$52.80	$52.80
Purchase #7	$149.32	6.163%	$158.5226	$158.52	$158.50	$158.50
7 purchase totals =	$728.13		$796.8555	$796.85	$796.80	$796.90