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	$44.99	11.413%	$50.1247	$50.12	$50.10	$50.10
Purchase #2	$249.34	10.410%	$275.2963	$275.30	$275.30	$275.30
Purchase #3	$71.47	9.831%	$78.4962	$78.50	$78.50	$78.50
Purchase #4	$34.99	8.238%	$37.8725	$37.87	$37.85	$37.90
Purchase #5	$212.41	7.759%	$228.8909	$228.89	$228.90	$228.90
Purchase #6	$91.44	4.390%	$95.4542	$95.45	$95.45	$95.50
Purchase #7	$11.64	13.116%	$13.1667	$13.17	$13.15	$13.20
7 purchase totals =	$716.28		$779.3015	$779.30	$779.25	$779.40