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	$249.41	6.147%	$264.7412	$264.74	$264.75	$264.70
Purchase #2	$141.78	3.332%	$146.5041	$146.50	$146.50	$146.50
Purchase #3	$90.46	9.741%	$99.2717	$99.27	$99.25	$99.30
Purchase #4	$51.30	13.603%	$58.2783	$58.28	$58.30	$58.30
Purchase #5	$57.74	13.608%	$65.5973	$65.60	$65.60	$65.60
Purchase #6	$102.81	13.676%	$116.8703	$116.87	$116.85	$116.90
Purchase #7	$24.90	3.503%	$25.7722	$25.77	$25.75	$25.80
7 purchase totals =	$718.40		$777.0351	$777.03	$777.00	$777.10