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	$83.59	8.599%	$90.7779	$90.78	$90.80	$90.80
Purchase #2	$169.55	5.827%	$179.4297	$179.43	$179.45	$179.40
Purchase #3	$219.74	6.464%	$233.944	$233.94	$233.95	$233.90
Purchase #4	$188.90	4.429%	$197.2664	$197.27	$197.25	$197.30
Purchase #5	$168.77	7.389%	$181.2404	$181.24	$181.25	$181.20
Purchase #6	$223.56	12.774%	$252.1176	$252.12	$252.10	$252.10
Purchase #7	$11.58	5.740%	$12.2447	$12.24	$12.25	$12.20
7 purchase totals =	$1,065.69		$1,147.0207	$1,147.02	$1,147.05	$1,146.90