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	$121.35	5.827%	$128.4211	$128.42	$128.40	$128.40
Purchase #2	$52.74	3.855%	$54.7731	$54.77	$54.75	$54.80
Purchase #3	$234.54	9.348%	$256.4648	$256.46	$256.45	$256.50
Purchase #4	$214.98	9.674%	$235.7772	$235.78	$235.80	$235.80
Purchase #5	$249.83	4.130%	$260.148	$260.15	$260.15	$260.10
Purchase #6	$71.88	8.739%	$78.1616	$78.16	$78.15	$78.20
Purchase #7	$18.95	8.216%	$20.5069	$20.51	$20.50	$20.50
7 purchase totals =	$964.27		$1,034.2527	$1,034.25	$1,034.20	$1,034.30