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	$195.31	4.667%	$204.4251	$204.43	$204.45	$204.40
Purchase #2	$69.52	13.124%	$78.6438	$78.64	$78.65	$78.60
Purchase #3	$76.56	11.434%	$85.3139	$85.31	$85.30	$85.30
Purchase #4	$57.77	13.562%	$65.6048	$65.60	$65.60	$65.60
Purchase #5	$188.27	10.265%	$207.5959	$207.60	$207.60	$207.60
Purchase #6	$46.56	7.687%	$50.1391	$50.14	$50.15	$50.10
Purchase #7	$141.76	6.149%	$150.4768	$150.48	$150.50	$150.50
7 purchase totals =	$775.75		$842.1994	$842.20	$842.25	$842.10