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	$55.32	11.668%	$61.7747	$61.77	$61.75	$61.80
Purchase #2	$103.83	11.811%	$116.0934	$116.09	$116.10	$116.10
Purchase #3	$122.87	12.808%	$138.6072	$138.61	$138.60	$138.60
Purchase #4	$77.69	6.873%	$83.0296	$83.03	$83.05	$83.00
Purchase #5	$120.85	12.790%	$136.3067	$136.31	$136.30	$136.30
Purchase #6	$127.52	3.848%	$132.427	$132.43	$132.45	$132.40
Purchase #7	$159.90	3.490%	$165.4805	$165.48	$165.50	$165.50
7 purchase totals =	$767.98		$833.7191	$833.72	$833.75	$833.70