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	$224.49	12.418%	$252.3672	$252.37	$252.35	$252.40
Purchase #2	$35.93	12.156%	$40.2977	$40.30	$40.30	$40.30
Purchase #3	$131.96	10.143%	$145.3447	$145.34	$145.35	$145.30
Purchase #4	$26.99	12.603%	$30.3915	$30.39	$30.40	$30.40
Purchase #5	$79.98	6.673%	$85.3171	$85.32	$85.30	$85.30
Purchase #6	$91.77	8.423%	$99.4998	$99.50	$99.50	$99.50
Purchase #7	$10.74	12.576%	$12.0907	$12.09	$12.10	$12.10
7 purchase totals =	$601.86		$665.3087	$665.31	$665.30	$665.30