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	$12.33	9.257%	$13.4714	$13.47	$13.45	$13.50
Purchase #2	$114.65	10.298%	$126.4567	$126.46	$126.45	$126.50
Purchase #3	$83.80	13.874%	$95.4264	$95.43	$95.45	$95.40
Purchase #4	$121.90	4.792%	$127.7414	$127.74	$127.75	$127.70
Purchase #5	$116.99	11.174%	$130.0625	$130.06	$130.05	$130.10
Purchase #6	$42.86	4.287%	$44.6974	$44.70	$44.70	$44.70
Purchase #7	$36.28	3.279%	$37.4696	$37.47	$37.45	$37.50
7 purchase totals =	$528.81		$575.3254	$575.33	$575.30	$575.40