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	$68.40	4.269%	$71.32	$71.32	$71.30	$71.30
Purchase #2	$84.53	5.563%	$89.2324	$89.23	$89.25	$89.20
Purchase #3	$164.55	4.865%	$172.5554	$172.56	$172.55	$172.60
Purchase #4	$169.56	6.784%	$181.063	$181.06	$181.05	$181.10
Purchase #5	$243.87	9.447%	$266.9084	$266.91	$266.90	$266.90
Purchase #6	$63.31	7.564%	$68.0988	$68.10	$68.10	$68.10
Purchase #7	$221.97	8.741%	$241.3724	$241.37	$241.35	$241.40
7 purchase totals =	$1,016.19		$1,090.5504	$1,090.55	$1,090.50	$1,090.60