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	$65.80	9.785%	$72.2385	$72.24	$72.25	$72.20
Purchase #2	$29.55	9.771%	$32.4373	$32.44	$32.45	$32.40
Purchase #3	$37.84	6.558%	$40.3215	$40.32	$40.30	$40.30
Purchase #4	$6.93	3.331%	$7.1608	$7.16	$7.15	$7.20
Purchase #5	$125.40	7.379%	$134.6533	$134.65	$134.65	$134.70
Purchase #6	$132.38	10.194%	$145.8748	$145.87	$145.85	$145.90
Purchase #7	$138.40	6.131%	$146.8853	$146.89	$146.90	$146.90
7 purchase totals =	$536.30		$579.5715	$579.57	$579.55	$579.60