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	$85.67	7.621%	$92.1989	$92.20	$92.20	$92.20
Purchase #2	$77.91	3.198%	$80.4016	$80.40	$80.40	$80.40
Purchase #3	$228.96	8.123%	$247.5584	$247.56	$247.55	$247.60
Purchase #4	$154.41	6.467%	$164.3957	$164.40	$164.40	$164.40
Purchase #5	$176.32	13.334%	$199.8305	$199.83	$199.85	$199.80
Purchase #6	$111.86	10.106%	$123.1646	$123.16	$123.15	$123.20
Purchase #7	$6.97	12.553%	$7.8449	$7.84	$7.85	$7.80
7 purchase totals =	$842.10		$915.3946	$915.39	$915.40	$915.40