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	$84.87	5.502%	$89.5395	$89.54	$89.55	$89.50
Purchase #2	$59.43	13.447%	$67.4216	$67.42	$67.40	$67.40
Purchase #3	$212.31	13.563%	$241.1056	$241.11	$241.10	$241.10
Purchase #4	$72.64	7.627%	$78.1803	$78.18	$78.20	$78.20
Purchase #5	$244.27	6.149%	$259.2902	$259.29	$259.30	$259.30
Purchase #6	$229.48	11.724%	$256.3842	$256.38	$256.40	$256.40
Purchase #7	$45.62	10.118%	$50.2358	$50.24	$50.25	$50.20
7 purchase totals =	$948.62		$1,042.1572	$1,042.16	$1,042.20	$1,042.10