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	$195.58	12.240%	$219.519	$219.52	$219.50	$219.50
Purchase #2	$72.69	8.549%	$78.9043	$78.90	$78.90	$78.90
Purchase #3	$138.65	13.405%	$157.236	$157.24	$157.25	$157.20
Purchase #4	$197.38	6.649%	$210.5038	$210.50	$210.50	$210.50
Purchase #5	$95.92	9.592%	$105.1206	$105.12	$105.10	$105.10
Purchase #6	$90.61	3.570%	$93.8448	$93.84	$93.85	$93.80
Purchase #7	$16.99	8.695%	$18.4673	$18.47	$18.45	$18.50
7 purchase totals =	$807.82		$883.5958	$883.59	$883.55	$883.50