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	$200.72	11.707%	$224.2183	$224.22	$224.20	$224.20
Purchase #2	$83.62	6.448%	$89.0118	$89.01	$89.00	$89.00
Purchase #3	$43.37	10.230%	$47.8068	$47.81	$47.80	$47.80
Purchase #4	$89.51	6.282%	$95.133	$95.13	$95.15	$95.10
Purchase #5	$73.78	3.849%	$76.6198	$76.62	$76.60	$76.60
Purchase #6	$161.29	11.422%	$179.7125	$179.71	$179.70	$179.70
Purchase #7	$58.69	9.867%	$64.4809	$64.48	$64.50	$64.50
7 purchase totals =	$710.98		$776.9831	$776.98	$776.95	$776.90