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	$38.40	12.640%	$43.2538	$43.25	$43.25	$43.30
Purchase #2	$159.69	4.322%	$166.5918	$166.59	$166.60	$166.60
Purchase #3	$206.48	11.763%	$230.7682	$230.77	$230.75	$230.80
Purchase #4	$210.30	8.111%	$227.3574	$227.36	$227.35	$227.40
Purchase #5	$82.46	8.234%	$89.2498	$89.25	$89.25	$89.20
Purchase #6	$76.46	13.105%	$86.4801	$86.48	$86.50	$86.50
Purchase #7	$142.84	11.684%	$159.5294	$159.53	$159.55	$159.50
7 purchase totals =	$916.63		$1,003.2305	$1,003.23	$1,003.25	$1,003.30