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	$175.48	5.730%	$185.535	$185.54	$185.55	$185.50
Purchase #2	$19.82	11.116%	$22.0232	$22.02	$22.00	$22.00
Purchase #3	$25.97	11.817%	$29.0389	$29.04	$29.05	$29.00
Purchase #4	$10.53	3.373%	$10.8852	$10.89	$10.90	$10.90
Purchase #5	$159.99	12.211%	$179.5264	$179.53	$179.55	$179.50
Purchase #6	$184.48	4.463%	$192.7133	$192.71	$192.70	$192.70
Purchase #7	$20.77	4.755%	$21.7576	$21.76	$21.75	$21.80
7 purchase totals =	$597.04		$641.4796	$641.49	$641.50	$641.40