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	$68.58	11.579%	$76.5209	$76.52	$76.50	$76.50
Purchase #2	$91.97	8.498%	$99.7856	$99.79	$99.80	$99.80
Purchase #3	$67.32	7.592%	$72.4309	$72.43	$72.45	$72.40
Purchase #4	$159.66	8.461%	$173.1688	$173.17	$173.15	$173.20
Purchase #5	$248.94	9.674%	$273.0225	$273.02	$273.00	$273.00
Purchase #6	$49.27	11.317%	$54.8459	$54.85	$54.85	$54.80
Purchase #7	$126.72	12.539%	$142.6094	$142.61	$142.60	$142.60
7 purchase totals =	$812.46		$892.3840	$892.39	$892.35	$892.30