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	$29.58	13.526%	$33.581	$33.58	$33.60	$33.60
Purchase #2	$131.61	9.806%	$144.5157	$144.52	$144.50	$144.50
Purchase #3	$169.91	13.300%	$192.508	$192.51	$192.50	$192.50
Purchase #4	$8.87	7.139%	$9.5032	$9.50	$9.50	$9.50
Purchase #5	$54.71	3.355%	$56.5455	$56.55	$56.55	$56.50
Purchase #6	$99.38	5.762%	$105.1063	$105.11	$105.10	$105.10
Purchase #7	$141.66	3.760%	$146.9864	$146.99	$147.00	$147.00
7 purchase totals =	$635.72		$688.7461	$688.76	$688.75	$688.70