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	$91.72	8.250%	$99.2869	$99.29	$99.30	$99.30
Purchase #2	$201.45	9.812%	$221.2163	$221.22	$221.20	$221.20
Purchase #3	$86.36	10.471%	$95.4028	$95.40	$95.40	$95.40
Purchase #4	$161.59	5.713%	$170.8216	$170.82	$170.80	$170.80
Purchase #5	$29.69	5.388%	$31.2897	$31.29	$31.30	$31.30
Purchase #6	$147.82	13.367%	$167.5791	$167.58	$167.60	$167.60
Purchase #7	$120.82	5.800%	$127.8276	$127.83	$127.85	$127.80
7 purchase totals =	$839.45		$913.4240	$913.43	$913.45	$913.40