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	$19.28	6.813%	$20.5935	$20.59	$20.60	$20.60
Purchase #2	$84.33	7.172%	$90.3781	$90.38	$90.40	$90.40
Purchase #3	$125.75	10.670%	$139.1675	$139.17	$139.15	$139.20
Purchase #4	$137.83	7.683%	$148.4195	$148.42	$148.40	$148.40
Purchase #5	$172.37	6.609%	$183.7619	$183.76	$183.75	$183.80
Purchase #6	$172.77	9.716%	$189.5563	$189.56	$189.55	$189.60
Purchase #7	$243.31	13.676%	$276.5851	$276.59	$276.60	$276.60
7 purchase totals =	$955.64		$1,048.4619	$1,048.47	$1,048.45	$1,048.60