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	$109.34	6.689%	$116.6538	$116.65	$116.65	$116.70
Purchase #2	$66.91	9.662%	$73.3748	$73.37	$73.35	$73.40
Purchase #3	$156.91	5.418%	$165.4114	$165.41	$165.40	$165.40
Purchase #4	$121.69	8.278%	$131.7635	$131.76	$131.75	$131.80
Purchase #5	$50.45	11.786%	$56.396	$56.40	$56.40	$56.40
Purchase #6	$111.99	12.729%	$126.2452	$126.25	$126.25	$126.20
Purchase #7	$83.81	8.550%	$90.9758	$90.98	$91.00	$91.00
7 purchase totals =	$701.10		$760.8205	$760.82	$760.80	$760.90