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	$67.60	4.391%	$70.5683	$70.57	$70.55	$70.60
Purchase #2	$67.43	13.739%	$76.6942	$76.69	$76.70	$76.70
Purchase #3	$176.43	6.302%	$187.5486	$187.55	$187.55	$187.50
Purchase #4	$101.94	3.118%	$105.1185	$105.12	$105.10	$105.10
Purchase #5	$146.84	3.850%	$152.4933	$152.49	$152.50	$152.50
Purchase #6	$133.56	4.386%	$139.4179	$139.42	$139.40	$139.40
Purchase #7	$129.49	13.462%	$146.9219	$146.92	$146.90	$146.90
7 purchase totals =	$823.29		$878.7627	$878.76	$878.70	$878.70