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	$187.79	10.810%	$208.0901	$208.09	$208.10	$208.10
Purchase #2	$170.37	5.728%	$180.1288	$180.13	$180.15	$180.10
Purchase #3	$50.97	13.436%	$57.8183	$57.82	$57.80	$57.80
Purchase #4	$30.76	5.680%	$32.5072	$32.51	$32.50	$32.50
Purchase #5	$24.46	3.659%	$25.355	$25.36	$25.35	$25.40
Purchase #6	$43.57	12.175%	$48.8746	$48.87	$48.85	$48.90
Purchase #7	$51.77	5.151%	$54.4367	$54.44	$54.45	$54.40
7 purchase totals =	$559.69		$607.2107	$607.22	$607.20	$607.20