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	$25.76	8.622%	$27.981	$27.98	$28.00	$28.00
Purchase #2	$88.81	8.262%	$96.1475	$96.15	$96.15	$96.10
Purchase #3	$153.34	10.457%	$169.3748	$169.37	$169.35	$169.40
Purchase #4	$173.64	9.303%	$189.7937	$189.79	$189.80	$189.80
Purchase #5	$138.74	8.240%	$150.1722	$150.17	$150.15	$150.20
Purchase #6	$119.92	12.172%	$134.5167	$134.52	$134.50	$134.50
Purchase #7	$131.60	8.265%	$142.4767	$142.48	$142.50	$142.50
7 purchase totals =	$831.81		$910.4626	$910.46	$910.45	$910.50