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	$80.48	10.678%	$89.0737	$89.07	$89.05	$89.10
Purchase #2	$162.98	10.244%	$179.6757	$179.68	$179.70	$179.70
Purchase #3	$51.59	3.551%	$53.422	$53.42	$53.40	$53.40
Purchase #4	$129.83	5.174%	$136.5474	$136.55	$136.55	$136.50
Purchase #5	$47.28	6.646%	$50.4222	$50.42	$50.40	$50.40
Purchase #6	$105.35	3.829%	$109.3839	$109.38	$109.40	$109.40
Purchase #7	$181.49	8.707%	$197.2923	$197.29	$197.30	$197.30
7 purchase totals =	$759.00		$815.8172	$815.81	$815.80	$815.80