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	$83.72	5.628%	$88.4318	$88.43	$88.45	$88.40
Purchase #2	$102.83	8.812%	$111.8914	$111.89	$111.90	$111.90
Purchase #3	$9.89	10.303%	$10.909	$10.91	$10.90	$10.90
Purchase #4	$153.90	7.268%	$165.0855	$165.09	$165.10	$165.10
Purchase #5	$164.79	4.318%	$171.9056	$171.91	$171.90	$171.90
Purchase #6	$72.90	7.138%	$78.1036	$78.10	$78.10	$78.10
Purchase #7	$144.77	13.832%	$164.7946	$164.79	$164.80	$164.80
7 purchase totals =	$732.80		$791.1215	$791.12	$791.15	$791.10