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	$214.51	12.105%	$240.4764	$240.48	$240.50	$240.50
Purchase #2	$151.85	12.375%	$170.6414	$170.64	$170.65	$170.60
Purchase #3	$216.77	11.598%	$241.911	$241.91	$241.90	$241.90
Purchase #4	$17.69	4.200%	$18.433	$18.43	$18.45	$18.40
Purchase #5	$113.65	13.309%	$128.7757	$128.78	$128.80	$128.80
Purchase #6	$183.36	7.317%	$196.7765	$196.78	$196.80	$196.80
Purchase #7	$211.48	7.842%	$228.0643	$228.06	$228.05	$228.10
7 purchase totals =	$1,109.31		$1,225.0783	$1,225.08	$1,225.15	$1,225.10