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	$82.33	8.839%	$89.6071	$89.61	$89.60	$89.60
Purchase #2	$92.58	11.573%	$103.2943	$103.29	$103.30	$103.30
Purchase #3	$38.62	6.196%	$41.0129	$41.01	$41.00	$41.00
Purchase #4	$66.99	13.786%	$76.2252	$76.23	$76.25	$76.20
Purchase #5	$67.48	4.136%	$70.271	$70.27	$70.25	$70.30
Purchase #6	$99.85	13.795%	$113.6243	$113.62	$113.60	$113.60
Purchase #7	$130.26	13.717%	$148.1278	$148.13	$148.15	$148.10
7 purchase totals =	$578.11		$642.1626	$642.16	$642.15	$642.10