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	$249.69	9.454%	$273.2957	$273.30	$273.30	$273.30
Purchase #2	$125.89	10.821%	$139.5126	$139.51	$139.50	$139.50
Purchase #3	$119.27	3.183%	$123.0664	$123.07	$123.05	$123.10
Purchase #4	$129.61	10.715%	$143.4977	$143.50	$143.50	$143.50
Purchase #5	$61.80	4.109%	$64.3394	$64.34	$64.35	$64.30
Purchase #6	$125.42	9.763%	$137.6648	$137.66	$137.65	$137.70
Purchase #7	$169.43	5.528%	$178.7961	$178.80	$178.80	$178.80
7 purchase totals =	$981.11		$1,060.1727	$1,060.18	$1,060.15	$1,060.20