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	$99.90	5.591%	$105.4854	$105.49	$105.50	$105.50
Purchase #2	$207.96	3.458%	$215.1513	$215.15	$215.15	$215.20
Purchase #3	$149.34	6.459%	$158.9859	$158.99	$159.00	$159.00
Purchase #4	$90.25	12.249%	$101.3047	$101.30	$101.30	$101.30
Purchase #5	$79.38	4.857%	$83.2355	$83.24	$83.25	$83.20
Purchase #6	$197.92	6.847%	$211.4716	$211.47	$211.45	$211.50
Purchase #7	$79.74	12.189%	$89.4595	$89.46	$89.45	$89.50
7 purchase totals =	$904.49		$965.0939	$965.10	$965.10	$965.20