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	$103.75	7.146%	$111.164	$111.16	$111.15	$111.20
Purchase #2	$129.94	3.365%	$134.3125	$134.31	$134.30	$134.30
Purchase #3	$67.65	5.812%	$71.5818	$71.58	$71.60	$71.60
Purchase #4	$58.37	9.127%	$63.6974	$63.70	$63.70	$63.70
Purchase #5	$123.33	6.820%	$131.7411	$131.74	$131.75	$131.70
Purchase #6	$137.70	3.679%	$142.766	$142.77	$142.75	$142.80
Purchase #7	$156.63	11.509%	$174.6565	$174.66	$174.65	$174.70
7 purchase totals =	$777.37		$829.9193	$829.92	$829.90	$830.00