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	$15.89	4.330%	$16.578	$16.58	$16.60	$16.60
Purchase #2	$69.79	13.850%	$79.4559	$79.46	$79.45	$79.50
Purchase #3	$40.88	11.177%	$45.4492	$45.45	$45.45	$45.40
Purchase #4	$218.31	6.651%	$232.8298	$232.83	$232.85	$232.80
Purchase #5	$74.91	3.306%	$77.3865	$77.39	$77.40	$77.40
Purchase #6	$48.94	10.832%	$54.2412	$54.24	$54.25	$54.20
Purchase #7	$79.34	7.534%	$85.3175	$85.32	$85.30	$85.30
7 purchase totals =	$548.06		$591.2581	$591.27	$591.30	$591.20