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	$250.32	4.591%	$261.8122	$261.81	$261.80	$261.80
Purchase #2	$167.57	9.146%	$182.896	$182.90	$182.90	$182.90
Purchase #3	$156.68	5.800%	$165.7674	$165.77	$165.75	$165.80
Purchase #4	$37.65	7.642%	$40.5272	$40.53	$40.55	$40.50
Purchase #5	$35.63	5.398%	$37.5533	$37.55	$37.55	$37.60
Purchase #6	$145.91	13.224%	$165.2051	$165.21	$165.20	$165.20
Purchase #7	$135.66	7.495%	$145.8277	$145.83	$145.85	$145.80
7 purchase totals =	$929.42		$999.5889	$999.60	$999.60	$999.60