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	$247.83	5.258%	$260.8609	$260.86	$260.85	$260.90
Purchase #2	$128.77	3.153%	$132.8301	$132.83	$132.85	$132.80
Purchase #3	$198.73	11.710%	$222.0013	$222.00	$222.00	$222.00
Purchase #4	$195.72	9.482%	$214.2782	$214.28	$214.30	$214.30
Purchase #5	$40.61	11.796%	$45.4004	$45.40	$45.40	$45.40
Purchase #6	$72.38	7.754%	$77.9923	$77.99	$78.00	$78.00
Purchase #7	$98.86	9.768%	$108.5166	$108.52	$108.50	$108.50
7 purchase totals =	$982.90		$1,061.8798	$1,061.88	$1,061.90	$1,061.90