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	$249.82	6.531%	$266.1357	$266.14	$266.15	$266.10
Purchase #2	$92.87	12.490%	$104.4695	$104.47	$104.45	$104.50
Purchase #3	$176.96	12.674%	$199.3879	$199.39	$199.40	$199.40
Purchase #4	$93.72	6.388%	$99.7068	$99.71	$99.70	$99.70
Purchase #5	$157.29	3.556%	$162.8832	$162.88	$162.90	$162.90
Purchase #6	$91.45	7.632%	$98.4295	$98.43	$98.45	$98.40
Purchase #7	$97.45	13.677%	$110.7782	$110.78	$110.80	$110.80
7 purchase totals =	$959.56		$1,041.7908	$1,041.80	$1,041.85	$1,041.80