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	$233.96	6.638%	$249.4903	$249.49	$249.50	$249.50
Purchase #2	$208.81	11.807%	$233.4642	$233.46	$233.45	$233.50
Purchase #3	$117.74	3.643%	$122.0293	$122.03	$122.05	$122.00
Purchase #4	$159.49	8.202%	$172.5714	$172.57	$172.55	$172.60
Purchase #5	$104.55	6.831%	$111.6918	$111.69	$111.70	$111.70
Purchase #6	$153.52	10.696%	$169.9405	$169.94	$169.95	$169.90
Purchase #7	$140.93	7.298%	$151.2151	$151.22	$151.20	$151.20
7 purchase totals =	$1,119.00		$1,210.4026	$1,210.40	$1,210.40	$1,210.40