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	$122.40	13.547%	$138.9815	$138.98	$139.00	$139.00
Purchase #2	$95.93	9.815%	$105.3455	$105.35	$105.35	$105.30
Purchase #3	$155.38	11.255%	$172.868	$172.87	$172.85	$172.90
Purchase #4	$212.59	12.191%	$238.5068	$238.51	$238.50	$238.50
Purchase #5	$128.69	6.233%	$136.7112	$136.71	$136.70	$136.70
Purchase #6	$90.79	4.771%	$95.1216	$95.12	$95.10	$95.10
Purchase #7	$135.36	4.806%	$141.8654	$141.87	$141.85	$141.90
7 purchase totals =	$941.14		$1,029.4000	$1,029.41	$1,029.35	$1,029.40