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	$238.29	5.210%	$250.7049	$250.70	$250.70	$250.70
Purchase #2	$151.43	13.856%	$172.4121	$172.41	$172.40	$172.40
Purchase #3	$171.73	11.700%	$191.8224	$191.82	$191.80	$191.80
Purchase #4	$173.31	9.838%	$190.3602	$190.36	$190.35	$190.40
Purchase #5	$168.70	12.391%	$189.6036	$189.60	$189.60	$189.60
Purchase #6	$167.32	4.328%	$174.5616	$174.56	$174.55	$174.60
Purchase #7	$158.47	13.567%	$179.9696	$179.97	$179.95	$180.00
7 purchase totals =	$1,229.25		$1,349.4344	$1,349.42	$1,349.35	$1,349.50