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	$208.87	7.468%	$224.4684	$224.47	$224.45	$224.50
Purchase #2	$205.86	13.614%	$233.8858	$233.89	$233.90	$233.90
Purchase #3	$108.47	13.463%	$123.0733	$123.07	$123.05	$123.10
Purchase #4	$223.56	12.102%	$250.6152	$250.62	$250.60	$250.60
Purchase #5	$249.90	8.359%	$270.7891	$270.79	$270.80	$270.80
Purchase #6	$135.40	13.855%	$154.1597	$154.16	$154.15	$154.20
Purchase #7	$30.93	4.496%	$32.3206	$32.32	$32.30	$32.30
7 purchase totals =	$1,162.99		$1,289.3121	$1,289.32	$1,289.25	$1,289.40