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	$179.41	4.449%	$187.392	$187.39	$187.40	$187.40
Purchase #2	$163.34	10.560%	$180.5887	$180.59	$180.60	$180.60
Purchase #3	$163.83	13.196%	$185.449	$185.45	$185.45	$185.40
Purchase #4	$19.65	3.465%	$20.3309	$20.33	$20.35	$20.30
Purchase #5	$31.39	13.490%	$35.6245	$35.62	$35.60	$35.60
Purchase #6	$196.81	11.162%	$218.7779	$218.78	$218.80	$218.80
Purchase #7	$53.78	4.245%	$56.063	$56.06	$56.05	$56.10
7 purchase totals =	$808.21		$884.2260	$884.22	$884.25	$884.20