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	$6.55	9.283%	$7.158	$7.16	$7.15	$7.20
Purchase #2	$238.61	8.304%	$258.4242	$258.42	$258.40	$258.40
Purchase #3	$132.84	13.654%	$150.978	$150.98	$151.00	$151.00
Purchase #4	$89.26	6.773%	$95.3056	$95.31	$95.30	$95.30
Purchase #5	$77.55	7.769%	$83.5749	$83.57	$83.55	$83.60
Purchase #6	$45.89	6.453%	$48.8513	$48.85	$48.85	$48.90
Purchase #7	$168.25	4.836%	$176.3866	$176.39	$176.40	$176.40
7 purchase totals =	$758.95		$820.6786	$820.68	$820.65	$820.80