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	$6.77	12.787%	$7.6357	$7.64	$7.65	$7.60
Purchase #2	$218.90	10.560%	$242.0158	$242.02	$242.00	$242.00
Purchase #3	$118.81	11.287%	$132.2201	$132.22	$132.20	$132.20
Purchase #4	$215.49	8.128%	$233.005	$233.01	$233.00	$233.00
Purchase #5	$220.33	4.303%	$229.8108	$229.81	$229.80	$229.80
Purchase #6	$157.49	6.146%	$167.1693	$167.17	$167.15	$167.20
Purchase #7	$48.82	11.847%	$54.6037	$54.60	$54.60	$54.60
7 purchase totals =	$986.61		$1,066.4604	$1,066.47	$1,066.40	$1,066.40