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	$15.25	9.647%	$16.7212	$16.72	$16.70	$16.70
Purchase #2	$172.38	8.740%	$187.446	$187.45	$187.45	$187.40
Purchase #3	$27.69	13.438%	$31.411	$31.41	$31.40	$31.40
Purchase #4	$199.76	11.866%	$223.4635	$223.46	$223.45	$223.50
Purchase #5	$144.73	5.367%	$152.4977	$152.50	$152.50	$152.50
Purchase #6	$9.86	6.710%	$10.5216	$10.52	$10.50	$10.50
Purchase #7	$32.98	3.291%	$34.0654	$34.07	$34.05	$34.10
7 purchase totals =	$602.65		$656.1264	$656.13	$656.05	$656.10