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	$53.43	10.476%	$59.0273	$59.03	$59.05	$59.00
Purchase #2	$79.43	8.567%	$86.2348	$86.23	$86.25	$86.20
Purchase #3	$107.89	11.637%	$120.4452	$120.45	$120.45	$120.40
Purchase #4	$144.54	13.754%	$164.42	$164.42	$164.40	$164.40
Purchase #5	$47.37	8.146%	$51.2288	$51.23	$51.25	$51.20
Purchase #6	$147.53	3.805%	$153.1435	$153.14	$153.15	$153.10
Purchase #7	$20.50	9.499%	$22.4473	$22.45	$22.45	$22.40
7 purchase totals =	$600.69		$656.9469	$656.95	$657.00	$656.70