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	$79.76	13.561%	$90.5763	$90.58	$90.60	$90.60
Purchase #2	$129.97	12.404%	$146.0915	$146.09	$146.10	$146.10
Purchase #3	$97.39	4.784%	$102.0491	$102.05	$102.05	$102.00
Purchase #4	$158.69	8.614%	$172.3596	$172.36	$172.35	$172.40
Purchase #5	$239.32	3.371%	$247.3875	$247.39	$247.40	$247.40
Purchase #6	$178.73	12.224%	$200.578	$200.58	$200.60	$200.60
Purchase #7	$76.97	12.442%	$86.5466	$86.55	$86.55	$86.50
7 purchase totals =	$960.83		$1,045.5886	$1,045.60	$1,045.65	$1,045.60