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	$77.45	3.738%	$80.3451	$80.35	$80.35	$80.30
Purchase #2	$224.88	13.458%	$255.1444	$255.14	$255.15	$255.10
Purchase #3	$109.32	5.745%	$115.6004	$115.60	$115.60	$115.60
Purchase #4	$60.60	8.811%	$65.9395	$65.94	$65.95	$65.90
Purchase #5	$171.39	7.640%	$184.4842	$184.48	$184.50	$184.50
Purchase #6	$20.35	12.256%	$22.8441	$22.84	$22.85	$22.80
Purchase #7	$65.31	9.194%	$71.3146	$71.31	$71.30	$71.30
7 purchase totals =	$729.30		$795.6723	$795.66	$795.70	$795.50