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	$26.80	11.519%	$29.8871	$29.89	$29.90	$29.90
Purchase #2	$119.92	6.369%	$127.5577	$127.56	$127.55	$127.60
Purchase #3	$177.84	7.347%	$190.9059	$190.91	$190.90	$190.90
Purchase #4	$104.89	7.861%	$113.1354	$113.14	$113.15	$113.10
Purchase #5	$171.94	3.808%	$178.4875	$178.49	$178.50	$178.50
Purchase #6	$51.99	7.848%	$56.0702	$56.07	$56.05	$56.10
Purchase #7	$227.34	11.662%	$253.8524	$253.85	$253.85	$253.90
7 purchase totals =	$880.72		$949.8962	$949.91	$949.90	$950.00