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	$142.92	8.581%	$155.184	$155.18	$155.20	$155.20
Purchase #2	$89.69	9.791%	$98.4715	$98.47	$98.45	$98.50
Purchase #3	$246.45	3.762%	$255.7214	$255.72	$255.70	$255.70
Purchase #4	$98.27	6.669%	$104.8236	$104.82	$104.80	$104.80
Purchase #5	$93.87	11.107%	$104.2961	$104.30	$104.30	$104.30
Purchase #6	$79.81	5.114%	$83.8915	$83.89	$83.90	$83.90
Purchase #7	$102.71	8.391%	$111.3284	$111.33	$111.35	$111.30
7 purchase totals =	$853.72		$913.7165	$913.71	$913.70	$913.70