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	$196.91	9.404%	$215.4274	$215.43	$215.45	$215.40
Purchase #2	$37.69	11.449%	$42.0051	$42.01	$42.00	$42.00
Purchase #3	$80.75	13.419%	$91.5858	$91.59	$91.60	$91.60
Purchase #4	$127.32	7.712%	$137.1389	$137.14	$137.15	$137.10
Purchase #5	$167.81	5.426%	$176.9154	$176.92	$176.90	$176.90
Purchase #6	$37.56	8.369%	$40.7034	$40.70	$40.70	$40.70
Purchase #7	$129.32	7.399%	$138.8884	$138.89	$138.90	$138.90
7 purchase totals =	$777.36		$842.6644	$842.68	$842.70	$842.60