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	$145.66	13.524%	$165.3591	$165.36	$165.35	$165.40
Purchase #2	$79.37	4.647%	$83.0583	$83.06	$83.05	$83.10
Purchase #3	$89.50	11.691%	$99.9634	$99.96	$99.95	$100.00
Purchase #4	$139.50	9.858%	$153.2519	$153.25	$153.25	$153.30
Purchase #5	$111.56	8.390%	$120.9199	$120.92	$120.90	$120.90
Purchase #6	$196.26	5.514%	$207.0818	$207.08	$207.10	$207.10
Purchase #7	$178.46	5.619%	$188.4877	$188.49	$188.50	$188.50
7 purchase totals =	$940.31		$1,018.1221	$1,018.12	$1,018.10	$1,018.30