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	$55.60	7.174%	$59.5887	$59.59	$59.60	$59.60
Purchase #2	$123.91	7.143%	$132.7609	$132.76	$132.75	$132.80
Purchase #3	$114.90	13.810%	$130.7677	$130.77	$130.75	$130.80
Purchase #4	$134.30	3.667%	$139.2248	$139.22	$139.20	$139.20
Purchase #5	$208.86	13.366%	$236.7762	$236.78	$236.80	$236.80
Purchase #6	$109.86	9.760%	$120.5823	$120.58	$120.60	$120.60
Purchase #7	$93.34	7.728%	$100.5533	$100.55	$100.55	$100.60
7 purchase totals =	$840.77		$920.2539	$920.25	$920.25	$920.40