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	$91.52	5.172%	$96.2534	$96.25	$96.25	$96.30
Purchase #2	$131.94	10.187%	$145.3807	$145.38	$145.40	$145.40
Purchase #3	$108.31	3.672%	$112.2871	$112.29	$112.30	$112.30
Purchase #4	$136.83	9.406%	$149.7002	$149.70	$149.70	$149.70
Purchase #5	$83.62	9.802%	$91.8164	$91.82	$91.80	$91.80
Purchase #6	$93.52	11.796%	$104.5516	$104.55	$104.55	$104.60
Purchase #7	$135.51	6.379%	$144.1542	$144.15	$144.15	$144.20
7 purchase totals =	$781.25		$844.1436	$844.14	$844.15	$844.30