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	$69.33	13.406%	$78.6244	$78.62	$78.60	$78.60
Purchase #2	$46.90	6.856%	$50.1155	$50.12	$50.10	$50.10
Purchase #3	$191.25	4.310%	$199.4929	$199.49	$199.50	$199.50
Purchase #4	$37.71	11.540%	$42.0617	$42.06	$42.05	$42.10
Purchase #5	$105.95	12.697%	$119.4025	$119.40	$119.40	$119.40
Purchase #6	$162.69	12.743%	$183.4216	$183.42	$183.40	$183.40
Purchase #7	$129.75	12.234%	$145.6236	$145.62	$145.60	$145.60
7 purchase totals =	$743.58		$818.7422	$818.73	$818.65	$818.70