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	$18.31	4.265%	$19.0909	$19.09	$19.10	$19.10
Purchase #2	$126.42	8.369%	$137.0001	$137.00	$137.00	$137.00
Purchase #3	$130.82	6.791%	$139.704	$139.70	$139.70	$139.70
Purchase #4	$148.90	6.157%	$158.0678	$158.07	$158.05	$158.10
Purchase #5	$99.33	8.260%	$107.5347	$107.53	$107.55	$107.50
Purchase #6	$85.30	6.115%	$90.5161	$90.52	$90.50	$90.50
Purchase #7	$131.38	3.218%	$135.6078	$135.61	$135.60	$135.60
7 purchase totals =	$740.46		$787.5214	$787.52	$787.50	$787.50