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	$141.79	9.636%	$155.4529	$155.45	$155.45	$155.50
Purchase #2	$9.46	12.839%	$10.6746	$10.67	$10.65	$10.70
Purchase #3	$159.90	12.541%	$179.9531	$179.95	$179.95	$180.00
Purchase #4	$153.46	12.802%	$173.1059	$173.11	$173.10	$173.10
Purchase #5	$82.47	11.138%	$91.6555	$91.66	$91.65	$91.70
Purchase #6	$109.88	5.582%	$116.0135	$116.01	$116.00	$116.00
Purchase #7	$166.96	3.109%	$172.1508	$172.15	$172.15	$172.20
7 purchase totals =	$823.92		$899.0063	$899.00	$898.95	$899.20