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	$153.56	7.347%	$164.8421	$164.84	$164.85	$164.80
Purchase #2	$186.60	13.472%	$211.7388	$211.74	$211.75	$211.70
Purchase #3	$148.78	8.400%	$161.2775	$161.28	$161.30	$161.30
Purchase #4	$17.75	12.594%	$19.9854	$19.99	$20.00	$20.00
Purchase #5	$85.78	5.276%	$90.3058	$90.31	$90.30	$90.30
Purchase #6	$15.35	11.682%	$17.1432	$17.14	$17.15	$17.10
Purchase #7	$73.82	6.235%	$78.4227	$78.42	$78.40	$78.40
7 purchase totals =	$681.64		$743.7155	$743.72	$743.75	$743.60