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	$33.53	13.721%	$38.1307	$38.13	$38.15	$38.10
Purchase #2	$190.29	12.846%	$214.7347	$214.73	$214.75	$214.70
Purchase #3	$108.70	13.286%	$123.1419	$123.14	$123.15	$123.10
Purchase #4	$83.26	4.564%	$87.06	$87.06	$87.05	$87.10
Purchase #5	$122.43	8.271%	$132.5562	$132.56	$132.55	$132.60
Purchase #6	$174.99	12.454%	$196.7833	$196.78	$196.80	$196.80
Purchase #7	$38.66	9.433%	$42.3068	$42.31	$42.30	$42.30
7 purchase totals =	$751.86		$834.7136	$834.71	$834.75	$834.70