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	$128.42	11.787%	$143.5569	$143.56	$143.55	$143.60
Purchase #2	$130.65	11.637%	$145.8537	$145.85	$145.85	$145.90
Purchase #3	$100.64	13.503%	$114.2294	$114.23	$114.25	$114.20
Purchase #4	$179.63	4.584%	$187.8642	$187.86	$187.85	$187.90
Purchase #5	$130.44	5.340%	$137.4055	$137.41	$137.40	$137.40
Purchase #6	$228.80	3.406%	$236.5929	$236.59	$236.60	$236.60
Purchase #7	$117.91	5.874%	$124.836	$124.84	$124.85	$124.80
7 purchase totals =	$1,016.49		$1,090.3386	$1,090.34	$1,090.35	$1,090.40