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	$169.54	6.670%	$180.8483	$180.85	$180.85	$180.80
Purchase #2	$80.82	7.182%	$86.6245	$86.62	$86.60	$86.60
Purchase #3	$120.38	8.674%	$130.8218	$130.82	$130.80	$130.80
Purchase #4	$49.31	10.496%	$54.4856	$54.49	$54.50	$54.50
Purchase #5	$166.97	4.404%	$174.3234	$174.32	$174.30	$174.30
Purchase #6	$134.54	13.738%	$153.0231	$153.02	$153.00	$153.00
Purchase #7	$10.77	13.134%	$12.1845	$12.18	$12.20	$12.20
7 purchase totals =	$732.33		$792.3112	$792.30	$792.25	$792.20