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	$169.38	10.603%	$187.3394	$187.34	$187.35	$187.30
Purchase #2	$163.57	6.172%	$173.6655	$173.67	$173.65	$173.70
Purchase #3	$156.75	10.312%	$172.9141	$172.91	$172.90	$172.90
Purchase #4	$203.78	3.354%	$210.6148	$210.61	$210.60	$210.60
Purchase #5	$90.89	12.424%	$102.1822	$102.18	$102.20	$102.20
Purchase #6	$71.40	3.196%	$73.6819	$73.68	$73.70	$73.70
Purchase #7	$78.61	9.380%	$85.9836	$85.98	$86.00	$86.00
7 purchase totals =	$934.38		$1,006.3815	$1,006.37	$1,006.40	$1,006.40