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	$123.25	6.789%	$131.6174	$131.62	$131.60	$131.60
Purchase #2	$55.50	4.205%	$57.8338	$57.83	$57.85	$57.80
Purchase #3	$154.31	5.360%	$162.581	$162.58	$162.60	$162.60
Purchase #4	$144.47	7.183%	$154.8473	$154.85	$154.85	$154.80
Purchase #5	$194.72	4.837%	$204.1386	$204.14	$204.15	$204.10
Purchase #6	$18.45	6.610%	$19.6695	$19.67	$19.65	$19.70
Purchase #7	$36.96	9.742%	$40.5606	$40.56	$40.55	$40.60
7 purchase totals =	$727.66		$771.2482	$771.25	$771.25	$771.20