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	$219.84	13.650%	$249.8482	$249.85	$249.85	$249.80
Purchase #2	$48.61	10.527%	$53.7272	$53.73	$53.75	$53.70
Purchase #3	$244.43	7.768%	$263.4173	$263.42	$263.40	$263.40
Purchase #4	$68.49	6.216%	$72.7473	$72.75	$72.75	$72.70
Purchase #5	$173.35	7.563%	$186.4605	$186.46	$186.45	$186.50
Purchase #6	$65.89	9.467%	$72.1278	$72.13	$72.15	$72.10
Purchase #7	$92.93	5.240%	$97.7995	$97.80	$97.80	$97.80
7 purchase totals =	$913.54		$996.1278	$996.14	$996.15	$996.00