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	$171.29	13.263%	$194.0082	$194.01	$194.00	$194.00
Purchase #2	$239.94	7.704%	$258.425	$258.43	$258.45	$258.40
Purchase #3	$37.75	8.534%	$40.9716	$40.97	$40.95	$41.00
Purchase #4	$107.66	9.408%	$117.7887	$117.79	$117.80	$117.80
Purchase #5	$185.46	3.263%	$191.5116	$191.51	$191.50	$191.50
Purchase #6	$50.89	12.585%	$57.2945	$57.29	$57.30	$57.30
Purchase #7	$28.44	10.617%	$31.4595	$31.46	$31.45	$31.50
7 purchase totals =	$821.43		$891.4591	$891.46	$891.45	$891.50