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	$37.79	13.267%	$42.8036	$42.80	$42.80	$42.80
Purchase #2	$83.91	6.364%	$89.25	$89.25	$89.25	$89.30
Purchase #3	$50.70	13.666%	$57.6287	$57.63	$57.65	$57.60
Purchase #4	$140.39	3.734%	$145.6322	$145.63	$145.65	$145.60
Purchase #5	$48.31	9.470%	$52.885	$52.89	$52.90	$52.90
Purchase #6	$26.63	12.102%	$29.8528	$29.85	$29.85	$29.90
Purchase #7	$236.47	10.669%	$261.699	$261.70	$261.70	$261.70
7 purchase totals =	$624.20		$679.7513	$679.75	$679.80	$679.80