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	$20.91	8.661%	$22.721	$22.72	$22.70	$22.70
Purchase #2	$172.44	7.529%	$185.423	$185.42	$185.40	$185.40
Purchase #3	$104.49	13.478%	$118.5732	$118.57	$118.55	$118.60
Purchase #4	$241.54	4.783%	$253.0929	$253.09	$253.10	$253.10
Purchase #5	$218.68	5.388%	$230.4625	$230.46	$230.45	$230.50
Purchase #6	$144.78	13.454%	$164.2587	$164.26	$164.25	$164.30
Purchase #7	$25.50	13.454%	$28.9308	$28.93	$28.95	$28.90
7 purchase totals =	$928.34		$1,003.4621	$1,003.45	$1,003.40	$1,003.50