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	$79.67	8.146%	$86.1599	$86.16	$86.15	$86.20
Purchase #2	$167.35	11.460%	$186.5283	$186.53	$186.55	$186.50
Purchase #3	$244.59	12.538%	$275.2567	$275.26	$275.25	$275.30
Purchase #4	$19.75	13.245%	$22.3659	$22.37	$22.35	$22.40
Purchase #5	$140.34	10.162%	$154.6014	$154.60	$154.60	$154.60
Purchase #6	$19.79	10.598%	$21.8873	$21.89	$21.90	$21.90
Purchase #7	$105.89	6.773%	$113.0619	$113.06	$113.05	$113.10
7 purchase totals =	$777.38		$859.8614	$859.87	$859.85	$860.00