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	$62.98	11.836%	$70.4343	$70.43	$70.45	$70.40
Purchase #2	$41.47	12.513%	$46.6591	$46.66	$46.65	$46.70
Purchase #3	$22.42	12.128%	$25.1391	$25.14	$25.15	$25.10
Purchase #4	$179.83	5.267%	$189.3016	$189.30	$189.30	$189.30
Purchase #5	$73.61	12.158%	$82.5595	$82.56	$82.55	$82.60
Purchase #6	$38.64	6.321%	$41.0824	$41.08	$41.10	$41.10
Purchase #7	$10.34	3.776%	$10.7304	$10.73	$10.75	$10.70
7 purchase totals =	$429.29		$465.9064	$465.90	$465.95	$465.90