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	$228.80	9.289%	$250.0532	$250.05	$250.05	$250.10
Purchase #2	$129.66	9.710%	$142.25	$142.25	$142.25	$142.30
Purchase #3	$183.88	4.646%	$192.4231	$192.42	$192.40	$192.40
Purchase #4	$134.49	4.538%	$140.5932	$140.59	$140.60	$140.60
Purchase #5	$188.25	13.688%	$214.0177	$214.02	$214.00	$214.00
Purchase #6	$34.64	7.307%	$37.1711	$37.17	$37.15	$37.20
Purchase #7	$145.89	3.745%	$151.3536	$151.35	$151.35	$151.40
7 purchase totals =	$1,045.61		$1,127.8619	$1,127.85	$1,127.80	$1,128.00