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	$36.44	6.367%	$38.7601	$38.76	$38.75	$38.80
Purchase #2	$242.41	12.810%	$273.4627	$273.46	$273.45	$273.50
Purchase #3	$154.94	10.637%	$171.421	$171.42	$171.40	$171.40
Purchase #4	$166.32	5.817%	$175.9948	$175.99	$176.00	$176.00
Purchase #5	$109.76	6.244%	$116.6134	$116.61	$116.60	$116.60
Purchase #6	$65.68	5.765%	$69.4665	$69.47	$69.45	$69.50
Purchase #7	$153.60	11.264%	$170.9015	$170.90	$170.90	$170.90
7 purchase totals =	$929.15		$1,016.6200	$1,016.61	$1,016.55	$1,016.70