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	$137.40	6.529%	$146.3708	$146.37	$146.35	$146.40
Purchase #2	$250.68	13.623%	$284.8301	$284.83	$284.85	$284.80
Purchase #3	$94.66	11.623%	$105.6623	$105.66	$105.65	$105.70
Purchase #4	$120.36	5.502%	$126.9822	$126.98	$127.00	$127.00
Purchase #5	$126.29	10.558%	$139.6237	$139.62	$139.60	$139.60
Purchase #6	$139.27	13.703%	$158.3542	$158.35	$158.35	$158.40
Purchase #7	$75.43	4.370%	$78.7263	$78.73	$78.75	$78.70
7 purchase totals =	$944.09		$1,040.5496	$1,040.54	$1,040.55	$1,040.60