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	$202.62	8.294%	$219.4253	$219.43	$219.45	$219.40
Purchase #2	$43.72	13.264%	$49.519	$49.52	$49.50	$49.50
Purchase #3	$58.98	12.803%	$66.5312	$66.53	$66.55	$66.50
Purchase #4	$12.47	10.760%	$13.8118	$13.81	$13.80	$13.80
Purchase #5	$28.93	12.500%	$32.5463	$32.55	$32.55	$32.50
Purchase #6	$113.82	12.204%	$127.7106	$127.71	$127.70	$127.70
Purchase #7	$35.75	3.795%	$37.1067	$37.11	$37.10	$37.10
7 purchase totals =	$496.29		$546.6509	$546.66	$546.65	$546.50