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	$101.67	9.330%	$111.1558	$111.16	$111.15	$111.20
Purchase #2	$172.31	6.139%	$182.8881	$182.89	$182.90	$182.90
Purchase #3	$168.66	3.116%	$173.9154	$173.92	$173.90	$173.90
Purchase #4	$234.37	10.743%	$259.5484	$259.55	$259.55	$259.50
Purchase #5	$130.25	7.416%	$139.9093	$139.91	$139.90	$139.90
Purchase #6	$115.46	11.552%	$128.7979	$128.80	$128.80	$128.80
Purchase #7	$163.57	11.359%	$182.1499	$182.15	$182.15	$182.10
7 purchase totals =	$1,086.29		$1,178.3648	$1,178.38	$1,178.35	$1,178.30