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	$241.83	4.119%	$251.791	$251.79	$251.80	$251.80
Purchase #2	$136.71	6.389%	$145.4444	$145.44	$145.45	$145.40
Purchase #3	$177.89	10.680%	$196.8887	$196.89	$196.90	$196.90
Purchase #4	$39.36	3.623%	$40.786	$40.79	$40.80	$40.80
Purchase #5	$209.50	7.772%	$225.7823	$225.78	$225.80	$225.80
Purchase #6	$45.54	11.460%	$50.7589	$50.76	$50.75	$50.80
Purchase #7	$117.65	11.457%	$131.1292	$131.13	$131.15	$131.10
7 purchase totals =	$968.48		$1,042.5805	$1,042.58	$1,042.65	$1,042.60