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	$17.47	7.849%	$18.8412	$18.84	$18.85	$18.80
Purchase #2	$63.59	13.346%	$72.0767	$72.08	$72.10	$72.10
Purchase #3	$97.35	6.381%	$103.5619	$103.56	$103.55	$103.60
Purchase #4	$175.33	6.170%	$186.1479	$186.15	$186.15	$186.10
Purchase #5	$222.26	13.391%	$252.0228	$252.02	$252.00	$252.00
Purchase #6	$57.89	12.864%	$65.337	$65.34	$65.35	$65.30
Purchase #7	$82.98	10.383%	$91.5958	$91.60	$91.60	$91.60
7 purchase totals =	$716.87		$789.5833	$789.59	$789.60	$789.50