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	$110.26	7.495%	$118.524	$118.52	$118.50	$118.50
Purchase #2	$124.53	11.540%	$138.9008	$138.90	$138.90	$138.90
Purchase #3	$246.71	13.507%	$280.0331	$280.03	$280.05	$280.00
Purchase #4	$91.56	11.793%	$102.3577	$102.36	$102.35	$102.40
Purchase #5	$11.25	6.176%	$11.9448	$11.94	$11.95	$11.90
Purchase #6	$122.27	4.126%	$127.3149	$127.31	$127.30	$127.30
Purchase #7	$6.89	5.746%	$7.2859	$7.29	$7.30	$7.30
7 purchase totals =	$713.47		$786.3612	$786.35	$786.35	$786.30