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	$170.48	5.507%	$179.8683	$179.87	$179.85	$179.90
Purchase #2	$185.42	11.705%	$207.1234	$207.12	$207.10	$207.10
Purchase #3	$81.50	9.591%	$89.3167	$89.32	$89.30	$89.30
Purchase #4	$36.90	6.862%	$39.4321	$39.43	$39.45	$39.40
Purchase #5	$106.77	12.346%	$119.9518	$119.95	$119.95	$120.00
Purchase #6	$204.44	5.664%	$216.0195	$216.02	$216.00	$216.00
Purchase #7	$99.92	5.268%	$105.1838	$105.18	$105.20	$105.20
7 purchase totals =	$885.43		$956.8956	$956.89	$956.85	$956.90