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	$158.77	4.523%	$165.9512	$165.95	$165.95	$166.00
Purchase #2	$132.42	6.701%	$141.2935	$141.29	$141.30	$141.30
Purchase #3	$34.77	4.277%	$36.2571	$36.26	$36.25	$36.30
Purchase #4	$154.72	6.809%	$165.2549	$165.25	$165.25	$165.30
Purchase #5	$113.42	4.464%	$118.4831	$118.48	$118.50	$118.50
Purchase #6	$137.83	10.847%	$152.7804	$152.78	$152.80	$152.80
Purchase #7	$87.85	3.440%	$90.872	$90.87	$90.85	$90.90
7 purchase totals =	$819.78		$870.8922	$870.88	$870.90	$871.10