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	$59.49	10.764%	$65.8935	$65.89	$65.90	$65.90
Purchase #2	$201.30	11.388%	$224.224	$224.22	$224.20	$224.20
Purchase #3	$80.61	3.719%	$83.6079	$83.61	$83.60	$83.60
Purchase #4	$29.71	5.789%	$31.4299	$31.43	$31.45	$31.40
Purchase #5	$50.77	10.717%	$56.211	$56.21	$56.20	$56.20
Purchase #6	$209.97	6.508%	$223.6348	$223.63	$223.65	$223.60
Purchase #7	$167.33	12.509%	$188.2613	$188.26	$188.25	$188.30
7 purchase totals =	$799.18		$873.2624	$873.25	$873.25	$873.20