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	$137.84	4.196%	$143.6238	$143.62	$143.60	$143.60
Purchase #2	$246.28	8.552%	$267.3419	$267.34	$267.35	$267.30
Purchase #3	$238.97	3.315%	$246.8919	$246.89	$246.90	$246.90
Purchase #4	$226.38	5.349%	$238.4891	$238.49	$238.50	$238.50
Purchase #5	$24.36	11.624%	$27.1916	$27.19	$27.20	$27.20
Purchase #6	$166.70	13.113%	$188.5594	$188.56	$188.55	$188.60
Purchase #7	$55.55	6.371%	$59.0891	$59.09	$59.10	$59.10
7 purchase totals =	$1,096.08		$1,171.1868	$1,171.18	$1,171.20	$1,171.20