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	$143.67	7.334%	$154.2068	$154.21	$154.20	$154.20
Purchase #2	$237.65	7.448%	$255.3502	$255.35	$255.35	$255.40
Purchase #3	$59.36	4.533%	$62.0508	$62.05	$62.05	$62.10
Purchase #4	$134.59	13.271%	$152.4514	$152.45	$152.45	$152.50
Purchase #5	$57.62	5.862%	$60.9977	$61.00	$61.00	$61.00
Purchase #6	$33.72	10.787%	$37.3574	$37.36	$37.35	$37.40
Purchase #7	$87.51	11.432%	$97.5141	$97.51	$97.50	$97.50
7 purchase totals =	$754.12		$819.9284	$819.93	$819.90	$820.10