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	$34.36	12.433%	$38.632	$38.63	$38.65	$38.60
Purchase #2	$58.89	11.615%	$65.7301	$65.73	$65.75	$65.70
Purchase #3	$79.40	13.470%	$90.0952	$90.10	$90.10	$90.10
Purchase #4	$78.60	3.434%	$81.2991	$81.30	$81.30	$81.30
Purchase #5	$211.56	10.570%	$233.9219	$233.92	$233.90	$233.90
Purchase #6	$175.73	9.521%	$192.4613	$192.46	$192.45	$192.50
Purchase #7	$53.37	4.627%	$55.8394	$55.84	$55.85	$55.80
7 purchase totals =	$691.91		$757.9790	$757.98	$758.00	$757.90