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	$10.80	11.642%	$12.0573	$12.06	$12.05	$12.10
Purchase #2	$230.58	8.562%	$250.3223	$250.32	$250.30	$250.30
Purchase #3	$165.76	3.556%	$171.6544	$171.65	$171.65	$171.70
Purchase #4	$133.95	12.563%	$150.7781	$150.78	$150.80	$150.80
Purchase #5	$79.30	5.467%	$83.6353	$83.64	$83.65	$83.60
Purchase #6	$160.72	13.206%	$181.9447	$181.94	$181.95	$181.90
Purchase #7	$97.91	11.779%	$109.4428	$109.44	$109.45	$109.40
7 purchase totals =	$879.02		$959.8349	$959.83	$959.85	$959.80