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	$35.48	10.621%	$39.2483	$39.25	$39.25	$39.20
Purchase #2	$144.77	8.807%	$157.5199	$157.52	$157.50	$157.50
Purchase #3	$18.34	12.340%	$20.6032	$20.60	$20.60	$20.60
Purchase #4	$143.85	10.475%	$158.9183	$158.92	$158.90	$158.90
Purchase #5	$52.99	9.718%	$58.1396	$58.14	$58.15	$58.10
Purchase #6	$50.78	6.717%	$54.1909	$54.19	$54.20	$54.20
Purchase #7	$64.34	12.324%	$72.2693	$72.27	$72.25	$72.30
7 purchase totals =	$510.55		$560.8895	$560.89	$560.85	$560.80