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	$127.78	8.294%	$138.3781	$138.38	$138.40	$138.40
Purchase #2	$83.33	7.808%	$89.8364	$89.84	$89.85	$89.80
Purchase #3	$153.76	11.302%	$171.138	$171.14	$171.15	$171.10
Purchase #4	$90.69	11.437%	$101.0622	$101.06	$101.05	$101.10
Purchase #5	$170.97	13.609%	$194.2373	$194.24	$194.25	$194.20
Purchase #6	$54.75	12.305%	$61.487	$61.49	$61.50	$61.50
Purchase #7	$22.39	9.107%	$24.4291	$24.43	$24.45	$24.40
7 purchase totals =	$703.67		$780.5681	$780.58	$780.65	$780.50