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	$107.50	10.617%	$118.9133	$118.91	$118.90	$118.90
Purchase #2	$68.55	11.260%	$76.2687	$76.27	$76.25	$76.30
Purchase #3	$32.55	4.176%	$33.9093	$33.91	$33.90	$33.90
Purchase #4	$235.90	9.390%	$258.051	$258.05	$258.05	$258.10
Purchase #5	$111.59	4.371%	$116.4676	$116.47	$116.45	$116.50
Purchase #6	$84.63	3.115%	$87.2662	$87.27	$87.25	$87.30
Purchase #7	$98.97	5.581%	$104.4935	$104.49	$104.50	$104.50
7 purchase totals =	$739.69		$795.3696	$795.37	$795.30	$795.50