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	$36.48	11.775%	$40.7755	$40.78	$40.80	$40.80
Purchase #2	$112.86	13.650%	$128.2654	$128.27	$128.25	$128.30
Purchase #3	$178.64	6.769%	$190.7321	$190.73	$190.75	$190.70
Purchase #4	$36.65	12.304%	$41.1594	$41.16	$41.15	$41.20
Purchase #5	$235.86	11.858%	$263.8283	$263.83	$263.85	$263.80
Purchase #6	$214.52	8.601%	$232.9709	$232.97	$232.95	$233.00
Purchase #7	$194.42	10.185%	$214.2217	$214.22	$214.20	$214.20
7 purchase totals =	$1,009.43		$1,111.9533	$1,111.96	$1,111.95	$1,112.00