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	$106.83	10.739%	$118.3025	$118.30	$118.30	$118.30
Purchase #2	$142.73	13.484%	$161.9757	$161.98	$162.00	$162.00
Purchase #3	$116.89	12.156%	$131.0991	$131.10	$131.10	$131.10
Purchase #4	$124.67	11.611%	$139.1454	$139.15	$139.15	$139.10
Purchase #5	$34.92	9.781%	$38.3355	$38.34	$38.35	$38.30
Purchase #6	$58.39	12.126%	$65.4704	$65.47	$65.45	$65.50
Purchase #7	$85.76	8.773%	$93.2837	$93.28	$93.30	$93.30
7 purchase totals =	$670.19		$747.6123	$747.62	$747.65	$747.60