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	$32.89	11.635%	$36.7168	$36.72	$36.70	$36.70
Purchase #2	$7.79	8.470%	$8.4498	$8.45	$8.45	$8.40
Purchase #3	$184.66	6.531%	$196.7201	$196.72	$196.70	$196.70
Purchase #4	$79.60	3.673%	$82.5237	$82.52	$82.50	$82.50
Purchase #5	$155.40	11.102%	$172.6525	$172.65	$172.65	$172.70
Purchase #6	$89.84	6.128%	$95.3454	$95.35	$95.35	$95.30
Purchase #7	$46.61	9.438%	$51.0091	$51.01	$51.00	$51.00
7 purchase totals =	$596.79		$643.4174	$643.42	$643.35	$643.30