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	$127.89	13.460%	$145.104	$145.10	$145.10	$145.10
Purchase #2	$152.58	13.137%	$172.6244	$172.62	$172.60	$172.60
Purchase #3	$234.34	11.506%	$261.3032	$261.30	$261.30	$261.30
Purchase #4	$243.39	7.819%	$262.4207	$262.42	$262.40	$262.40
Purchase #5	$153.86	11.466%	$171.5016	$171.50	$171.50	$171.50
Purchase #6	$231.74	5.618%	$244.7592	$244.76	$244.75	$244.80
Purchase #7	$250.25	3.129%	$258.0803	$258.08	$258.10	$258.10
7 purchase totals =	$1,394.05		$1,515.7934	$1,515.78	$1,515.75	$1,515.80