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	$20.52	11.580%	$22.8962	$22.90	$22.90	$22.90
Purchase #2	$153.85	7.132%	$164.8226	$164.82	$164.80	$164.80
Purchase #3	$33.48	13.225%	$37.9077	$37.91	$37.90	$37.90
Purchase #4	$173.48	8.588%	$188.3785	$188.38	$188.40	$188.40
Purchase #5	$79.59	5.244%	$83.7637	$83.76	$83.75	$83.80
Purchase #6	$108.33	4.387%	$113.0824	$113.08	$113.10	$113.10
Purchase #7	$241.35	5.463%	$254.535	$254.54	$254.55	$254.50
7 purchase totals =	$810.60		$865.3861	$865.39	$865.40	$865.40