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	$229.38	9.189%	$250.4577	$250.46	$250.45	$250.50
Purchase #2	$16.37	11.192%	$18.2021	$18.20	$18.20	$18.20
Purchase #3	$20.44	3.196%	$21.0933	$21.09	$21.10	$21.10
Purchase #4	$162.82	6.251%	$172.9979	$173.00	$173.00	$173.00
Purchase #5	$86.68	11.741%	$96.8571	$96.86	$96.85	$96.90
Purchase #6	$16.83	10.306%	$18.5645	$18.56	$18.55	$18.60
Purchase #7	$91.44	9.785%	$100.3874	$100.39	$100.40	$100.40
7 purchase totals =	$623.96		$678.5600	$678.56	$678.55	$678.70