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	$143.59	3.381%	$148.4448	$148.44	$148.45	$148.40
Purchase #2	$37.79	11.468%	$42.1238	$42.12	$42.10	$42.10
Purchase #3	$172.84	6.134%	$183.442	$183.44	$183.45	$183.40
Purchase #4	$106.71	7.354%	$114.5575	$114.56	$114.55	$114.60
Purchase #5	$164.60	5.335%	$173.3814	$173.38	$173.40	$173.40
Purchase #6	$46.29	9.659%	$50.7612	$50.76	$50.75	$50.80
Purchase #7	$31.53	5.525%	$33.272	$33.27	$33.25	$33.30
7 purchase totals =	$703.35		$745.9827	$745.97	$745.95	$746.00