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	$37.41	10.336%	$41.2767	$41.28	$41.30	$41.30
Purchase #2	$133.26	9.737%	$146.2355	$146.24	$146.25	$146.20
Purchase #3	$176.51	11.386%	$196.6074	$196.61	$196.60	$196.60
Purchase #4	$195.83	13.629%	$222.5197	$222.52	$222.50	$222.50
Purchase #5	$153.65	11.679%	$171.5948	$171.59	$171.60	$171.60
Purchase #6	$72.27	5.599%	$76.3164	$76.32	$76.30	$76.30
Purchase #7	$14.59	5.354%	$15.3711	$15.37	$15.35	$15.40
7 purchase totals =	$783.52		$869.9216	$869.93	$869.90	$869.90