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	$69.67	9.260%	$76.1214	$76.12	$76.10	$76.10
Purchase #2	$46.37	4.500%	$48.4567	$48.46	$48.45	$48.50
Purchase #3	$39.89	3.657%	$41.3488	$41.35	$41.35	$41.30
Purchase #4	$96.42	9.556%	$105.6339	$105.63	$105.65	$105.60
Purchase #5	$49.92	12.649%	$56.2344	$56.23	$56.25	$56.20
Purchase #6	$167.65	11.557%	$187.0253	$187.03	$187.05	$187.00
Purchase #7	$37.89	6.283%	$40.2706	$40.27	$40.25	$40.30
7 purchase totals =	$507.81		$555.0911	$555.09	$555.10	$555.00