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	$74.62	7.757%	$80.4083	$80.41	$80.40	$80.40
Purchase #2	$54.65	12.415%	$61.4348	$61.43	$61.45	$61.40
Purchase #3	$234.30	3.725%	$243.0277	$243.03	$243.05	$243.00
Purchase #4	$153.96	13.227%	$174.3243	$174.32	$174.30	$174.30
Purchase #5	$153.45	4.211%	$159.9118	$159.91	$159.90	$159.90
Purchase #6	$125.60	5.247%	$132.1902	$132.19	$132.20	$132.20
Purchase #7	$79.60	12.577%	$89.6113	$89.61	$89.60	$89.60
7 purchase totals =	$876.18		$940.9084	$940.90	$940.90	$940.80