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	$16.52	4.699%	$17.2963	$17.30	$17.30	$17.30
Purchase #2	$181.27	4.709%	$189.806	$189.81	$189.80	$189.80
Purchase #3	$184.81	3.702%	$191.6517	$191.65	$191.65	$191.70
Purchase #4	$197.49	3.595%	$204.5898	$204.59	$204.60	$204.60
Purchase #5	$72.85	7.696%	$78.4565	$78.46	$78.45	$78.50
Purchase #6	$29.54	9.243%	$32.2704	$32.27	$32.25	$32.30
Purchase #7	$88.47	12.393%	$99.4341	$99.43	$99.45	$99.40
7 purchase totals =	$770.95		$813.5048	$813.51	$813.50	$813.60