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	$77.82	7.287%	$83.4907	$83.49	$83.50	$83.50
Purchase #2	$64.77	5.866%	$68.5694	$68.57	$68.55	$68.60
Purchase #3	$118.29	7.477%	$127.1345	$127.13	$127.15	$127.10
Purchase #4	$228.93	12.868%	$258.3887	$258.39	$258.40	$258.40
Purchase #5	$79.79	8.457%	$86.5378	$86.54	$86.55	$86.50
Purchase #6	$233.82	6.709%	$249.507	$249.51	$249.50	$249.50
Purchase #7	$110.50	11.191%	$122.8661	$122.87	$122.85	$122.90
7 purchase totals =	$913.92		$996.4942	$996.50	$996.50	$996.50