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	$178.79	7.133%	$191.5431	$191.54	$191.55	$191.50
Purchase #2	$78.47	6.739%	$83.7581	$83.76	$83.75	$83.80
Purchase #3	$109.47	12.589%	$123.2512	$123.25	$123.25	$123.30
Purchase #4	$149.52	8.671%	$162.4849	$162.48	$162.50	$162.50
Purchase #5	$12.36	3.616%	$12.8069	$12.81	$12.80	$12.80
Purchase #6	$170.82	12.763%	$192.6218	$192.62	$192.60	$192.60
Purchase #7	$128.75	11.301%	$143.3	$143.30	$143.30	$143.30
7 purchase totals =	$828.18		$909.7660	$909.76	$909.75	$909.80