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	$63.69	10.182%	$70.1749	$70.17	$70.15	$70.20
Purchase #2	$179.83	9.271%	$196.502	$196.50	$196.50	$196.50
Purchase #3	$33.74	4.312%	$35.1949	$35.19	$35.20	$35.20
Purchase #4	$147.30	13.485%	$167.1634	$167.16	$167.15	$167.20
Purchase #5	$131.52	8.832%	$143.1358	$143.14	$143.15	$143.10
Purchase #6	$141.88	11.209%	$157.7833	$157.78	$157.80	$157.80
Purchase #7	$124.94	5.284%	$131.5418	$131.54	$131.55	$131.50
7 purchase totals =	$822.90		$901.4961	$901.48	$901.50	$901.50