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	$130.82	12.361%	$146.9907	$146.99	$147.00	$147.00
Purchase #2	$94.90	10.592%	$104.9518	$104.95	$104.95	$105.00
Purchase #3	$118.61	13.365%	$134.4622	$134.46	$134.45	$134.50
Purchase #4	$91.78	5.149%	$96.5058	$96.51	$96.50	$96.50
Purchase #5	$233.37	13.318%	$264.4502	$264.45	$264.45	$264.50
Purchase #6	$167.85	10.583%	$185.6136	$185.61	$185.60	$185.60
Purchase #7	$52.81	8.407%	$57.2497	$57.25	$57.25	$57.20
7 purchase totals =	$890.14		$990.2240	$990.22	$990.20	$990.30