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	$113.91	12.265%	$127.8811	$127.88	$127.90	$127.90
Purchase #2	$53.53	12.864%	$60.4161	$60.42	$60.40	$60.40
Purchase #3	$146.72	10.421%	$162.0097	$162.01	$162.00	$162.00
Purchase #4	$29.49	11.524%	$32.8884	$32.89	$32.90	$32.90
Purchase #5	$85.93	3.832%	$89.2228	$89.22	$89.20	$89.20
Purchase #6	$49.89	11.490%	$55.6224	$55.62	$55.60	$55.60
Purchase #7	$97.93	4.277%	$102.1185	$102.12	$102.10	$102.10
7 purchase totals =	$577.40		$630.1590	$630.16	$630.10	$630.10