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	$193.63	8.364%	$209.8252	$209.83	$209.85	$209.80
Purchase #2	$134.89	3.138%	$139.1228	$139.12	$139.10	$139.10
Purchase #3	$129.48	6.671%	$138.1176	$138.12	$138.10	$138.10
Purchase #4	$219.74	8.700%	$238.8574	$238.86	$238.85	$238.90
Purchase #5	$128.92	11.711%	$144.0178	$144.02	$144.00	$144.00
Purchase #6	$28.84	13.553%	$32.7487	$32.75	$32.75	$32.70
Purchase #7	$34.28	11.208%	$38.1221	$38.12	$38.10	$38.10
7 purchase totals =	$869.78		$940.8116	$940.82	$940.75	$940.70