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	$80.36	11.505%	$89.6054	$89.61	$89.60	$89.60
Purchase #2	$66.60	8.734%	$72.4168	$72.42	$72.40	$72.40
Purchase #3	$46.82	7.524%	$50.3427	$50.34	$50.35	$50.30
Purchase #4	$207.49	9.866%	$227.961	$227.96	$227.95	$228.00
Purchase #5	$137.75	5.197%	$144.9089	$144.91	$144.90	$144.90
Purchase #6	$194.59	4.608%	$203.5567	$203.56	$203.55	$203.60
Purchase #7	$136.49	11.395%	$152.043	$152.04	$152.05	$152.00
7 purchase totals =	$870.10		$940.8345	$940.84	$940.80	$940.80