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	$179.54	3.613%	$186.0268	$186.03	$186.05	$186.00
Purchase #2	$160.93	7.561%	$173.0979	$173.10	$173.10	$173.10
Purchase #3	$37.42	13.513%	$42.4766	$42.48	$42.50	$42.50
Purchase #4	$250.83	9.226%	$273.9716	$273.97	$273.95	$274.00
Purchase #5	$146.78	3.477%	$151.8835	$151.88	$151.90	$151.90
Purchase #6	$9.95	3.362%	$10.2845	$10.28	$10.30	$10.30
Purchase #7	$31.55	5.833%	$33.3903	$33.39	$33.40	$33.40
7 purchase totals =	$817.00		$871.1312	$871.13	$871.20	$871.20