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	$207.46	4.539%	$216.8766	$216.88	$216.90	$216.90
Purchase #2	$107.98	10.659%	$119.4896	$119.49	$119.50	$119.50
Purchase #3	$63.46	7.254%	$68.0634	$68.06	$68.05	$68.10
Purchase #4	$216.90	11.318%	$241.4487	$241.45	$241.45	$241.40
Purchase #5	$100.30	9.580%	$109.9087	$109.91	$109.90	$109.90
Purchase #6	$18.82	8.670%	$20.4517	$20.45	$20.45	$20.50
Purchase #7	$144.81	4.777%	$151.7276	$151.73	$151.75	$151.70
7 purchase totals =	$859.73		$927.9663	$927.97	$928.00	$928.00