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	$77.65	12.188%	$87.114	$87.11	$87.10	$87.10
Purchase #2	$129.88	3.562%	$134.5063	$134.51	$134.50	$134.50
Purchase #3	$131.82	10.761%	$146.0052	$146.01	$146.00	$146.00
Purchase #4	$158.49	6.166%	$168.2625	$168.26	$168.25	$168.30
Purchase #5	$220.31	6.476%	$234.5773	$234.58	$234.60	$234.60
Purchase #6	$86.61	9.144%	$94.5296	$94.53	$94.55	$94.50
Purchase #7	$41.96	4.204%	$43.724	$43.72	$43.70	$43.70
7 purchase totals =	$846.72		$908.7189	$908.72	$908.70	$908.70