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	$13.53	11.583%	$15.0972	$15.10	$15.10	$15.10
Purchase #2	$156.95	4.830%	$164.5307	$164.53	$164.55	$164.50
Purchase #3	$57.98	5.233%	$61.0141	$61.01	$61.00	$61.00
Purchase #4	$37.47	9.728%	$41.1151	$41.12	$41.10	$41.10
Purchase #5	$134.25	8.361%	$145.4746	$145.47	$145.45	$145.50
Purchase #6	$13.42	11.133%	$14.914	$14.91	$14.90	$14.90
Purchase #7	$12.69	9.619%	$13.9107	$13.91	$13.90	$13.90
7 purchase totals =	$426.29		$456.0564	$456.05	$456.00	$456.00