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	$19.33	9.295%	$21.1267	$21.13	$21.15	$21.10
Purchase #2	$116.92	12.564%	$131.6098	$131.61	$131.60	$131.60
Purchase #3	$78.26	4.530%	$81.8052	$81.81	$81.80	$81.80
Purchase #4	$61.30	13.813%	$69.7674	$69.77	$69.75	$69.80
Purchase #5	$46.76	9.554%	$51.2275	$51.23	$51.25	$51.20
Purchase #6	$85.29	11.280%	$94.9107	$94.91	$94.90	$94.90
Purchase #7	$102.47	6.174%	$108.7965	$108.80	$108.80	$108.80
7 purchase totals =	$510.33		$559.2438	$559.26	$559.25	$559.20