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	$9.40	12.608%	$10.5852	$10.59	$10.60	$10.60
Purchase #2	$7.87	9.174%	$8.592	$8.59	$8.60	$8.60
Purchase #3	$6.36	9.268%	$6.9494	$6.95	$6.95	$6.90
Purchase #4	$40.40	11.628%	$45.0977	$45.10	$45.10	$45.10
Purchase #5	$78.45	5.613%	$82.8534	$82.85	$82.85	$82.90
Purchase #6	$126.83	7.159%	$135.9098	$135.91	$135.90	$135.90
Purchase #7	$233.69	4.801%	$244.9095	$244.91	$244.90	$244.90
7 purchase totals =	$503.00		$534.8970	$534.90	$534.90	$534.90