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	$170.83	3.224%	$176.3376	$176.34	$176.35	$176.30
Purchase #2	$47.33	11.554%	$52.7985	$52.80	$52.80	$52.80
Purchase #3	$92.83	12.349%	$104.2936	$104.29	$104.30	$104.30
Purchase #4	$163.58	5.235%	$172.1434	$172.14	$172.15	$172.10
Purchase #5	$152.89	8.643%	$166.1043	$166.10	$166.10	$166.10
Purchase #6	$111.94	11.251%	$124.5344	$124.53	$124.55	$124.50
Purchase #7	$175.57	3.593%	$181.8782	$181.88	$181.90	$181.90
7 purchase totals =	$914.97		$978.0900	$978.08	$978.15	$978.00