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	$126.54	12.552%	$142.4233	$142.42	$142.40	$142.40
Purchase #2	$21.80	12.495%	$24.5239	$24.52	$24.50	$24.50
Purchase #3	$94.38	12.157%	$105.8538	$105.85	$105.85	$105.90
Purchase #4	$8.89	5.421%	$9.3719	$9.37	$9.35	$9.40
Purchase #5	$11.42	7.280%	$12.2514	$12.25	$12.25	$12.30
Purchase #6	$105.30	13.108%	$119.1027	$119.10	$119.10	$119.10
Purchase #7	$121.73	12.670%	$137.1532	$137.15	$137.15	$137.20
7 purchase totals =	$490.06		$550.6802	$550.66	$550.60	$550.80