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	$90.79	9.657%	$99.5576	$99.56	$99.55	$99.60
Purchase #2	$45.58	3.816%	$47.3193	$47.32	$47.30	$47.30
Purchase #3	$141.27	6.265%	$150.1206	$150.12	$150.10	$150.10
Purchase #4	$172.26	8.193%	$186.3733	$186.37	$186.35	$186.40
Purchase #5	$175.44	11.819%	$196.1753	$196.18	$196.20	$196.20
Purchase #6	$48.83	12.611%	$54.988	$54.99	$55.00	$55.00
Purchase #7	$24.55	8.143%	$26.5491	$26.55	$26.55	$26.50
7 purchase totals =	$698.72		$761.0832	$761.09	$761.05	$761.10