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	$29.83	8.370%	$32.3268	$32.33	$32.35	$32.30
Purchase #2	$223.80	13.641%	$254.3286	$254.33	$254.35	$254.30
Purchase #3	$245.82	7.622%	$264.5564	$264.56	$264.55	$264.60
Purchase #4	$138.38	13.797%	$157.4723	$157.47	$157.45	$157.50
Purchase #5	$85.67	10.315%	$94.5069	$94.51	$94.50	$94.50
Purchase #6	$175.96	5.368%	$185.4055	$185.41	$185.40	$185.40
Purchase #7	$100.86	9.679%	$110.6222	$110.62	$110.60	$110.60
7 purchase totals =	$1,000.32		$1,099.2187	$1,099.23	$1,099.20	$1,099.20