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	$14.90	6.780%	$15.9102	$15.91	$15.90	$15.90
Purchase #2	$109.42	10.367%	$120.7636	$120.76	$120.75	$120.80
Purchase #3	$94.35	11.874%	$105.5531	$105.55	$105.55	$105.60
Purchase #4	$132.40	9.328%	$144.7503	$144.75	$144.75	$144.80
Purchase #5	$133.86	9.406%	$146.4509	$146.45	$146.45	$146.50
Purchase #6	$71.50	8.601%	$77.6497	$77.65	$77.65	$77.60
Purchase #7	$228.39	12.428%	$256.7743	$256.77	$256.75	$256.80
7 purchase totals =	$784.82		$867.8521	$867.84	$867.80	$868.00