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	$63.89	13.392%	$72.4461	$72.45	$72.45	$72.40
Purchase #2	$246.86	4.155%	$257.117	$257.12	$257.10	$257.10
Purchase #3	$141.25	6.830%	$150.8974	$150.90	$150.90	$150.90
Purchase #4	$95.30	9.781%	$104.6213	$104.62	$104.60	$104.60
Purchase #5	$45.42	5.363%	$47.8559	$47.86	$47.85	$47.90
Purchase #6	$85.75	11.163%	$95.3223	$95.32	$95.30	$95.30
Purchase #7	$237.34	7.385%	$254.8676	$254.87	$254.85	$254.90
7 purchase totals =	$915.81		$983.1276	$983.14	$983.05	$983.10