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	$18.32	5.204%	$19.2734	$19.27	$19.25	$19.30
Purchase #2	$40.34	3.131%	$41.603	$41.60	$41.60	$41.60
Purchase #3	$71.75	6.303%	$76.2724	$76.27	$76.25	$76.30
Purchase #4	$124.48	9.713%	$136.5707	$136.57	$136.55	$136.60
Purchase #5	$78.49	13.443%	$89.0414	$89.04	$89.05	$89.00
Purchase #6	$233.68	6.103%	$247.9415	$247.94	$247.95	$247.90
Purchase #7	$208.64	9.609%	$228.6882	$228.69	$228.70	$228.70
7 purchase totals =	$775.70		$839.3906	$839.38	$839.35	$839.40