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	$16.83	11.200%	$18.715	$18.72	$18.70	$18.70
Purchase #2	$200.79	11.127%	$223.1319	$223.13	$223.15	$223.10
Purchase #3	$118.90	10.180%	$131.004	$131.00	$131.00	$131.00
Purchase #4	$197.93	5.154%	$208.1313	$208.13	$208.15	$208.10
Purchase #5	$131.54	9.331%	$143.814	$143.81	$143.80	$143.80
Purchase #6	$133.49	8.492%	$144.826	$144.83	$144.85	$144.80
Purchase #7	$236.42	11.690%	$264.0575	$264.06	$264.05	$264.10
7 purchase totals =	$1,035.90		$1,133.6797	$1,133.68	$1,133.70	$1,133.60