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	$34.33	6.577%	$36.5879	$36.59	$36.60	$36.60
Purchase #2	$68.92	11.111%	$76.5777	$76.58	$76.60	$76.60
Purchase #3	$245.86	13.559%	$279.1962	$279.20	$279.20	$279.20
Purchase #4	$120.98	8.864%	$131.7037	$131.70	$131.70	$131.70
Purchase #5	$67.30	8.113%	$72.76	$72.76	$72.75	$72.80
Purchase #6	$205.32	8.186%	$222.1275	$222.13	$222.15	$222.10
Purchase #7	$75.83	10.723%	$83.9613	$83.96	$83.95	$84.00
7 purchase totals =	$818.54		$902.9143	$902.92	$902.95	$903.00