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	$135.58	13.710%	$154.168	$154.17	$154.15	$154.20
Purchase #2	$228.42	10.145%	$251.5932	$251.59	$251.60	$251.60
Purchase #3	$64.48	12.320%	$72.4239	$72.42	$72.40	$72.40
Purchase #4	$133.39	4.202%	$138.995	$139.00	$139.00	$139.00
Purchase #5	$125.91	10.399%	$139.0034	$139.00	$139.00	$139.00
Purchase #6	$136.36	5.538%	$143.9116	$143.91	$143.90	$143.90
Purchase #7	$13.95	10.668%	$15.4382	$15.44	$15.45	$15.40
7 purchase totals =	$838.09		$915.5333	$915.53	$915.50	$915.50