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	$12.66	7.562%	$13.6173	$13.62	$13.60	$13.60
Purchase #2	$85.71	6.676%	$91.432	$91.43	$91.45	$91.40
Purchase #3	$49.76	11.725%	$55.5944	$55.59	$55.60	$55.60
Purchase #4	$115.65	13.539%	$131.3079	$131.31	$131.30	$131.30
Purchase #5	$51.32	7.150%	$54.9894	$54.99	$55.00	$55.00
Purchase #6	$16.45	8.834%	$17.9032	$17.90	$17.90	$17.90
Purchase #7	$29.34	10.810%	$32.5117	$32.51	$32.50	$32.50
7 purchase totals =	$360.89		$397.3559	$397.35	$397.35	$397.30