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	$70.83	13.360%	$80.2929	$80.29	$80.30	$80.30
Purchase #2	$104.68	6.478%	$111.4612	$111.46	$111.45	$111.50
Purchase #3	$85.91	6.472%	$91.4701	$91.47	$91.45	$91.50
Purchase #4	$149.49	5.151%	$157.1902	$157.19	$157.20	$157.20
Purchase #5	$157.79	11.854%	$176.4944	$176.49	$176.50	$176.50
Purchase #6	$151.37	11.640%	$168.9895	$168.99	$169.00	$169.00
Purchase #7	$200.50	9.541%	$219.6297	$219.63	$219.65	$219.60
7 purchase totals =	$920.57		$1,005.5280	$1,005.52	$1,005.55	$1,005.60