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	$238.63	10.632%	$264.0011	$264.00	$264.00	$264.00
Purchase #2	$37.53	5.271%	$39.5082	$39.51	$39.50	$39.50
Purchase #3	$12.54	11.484%	$13.9801	$13.98	$14.00	$14.00
Purchase #4	$226.54	6.396%	$241.0295	$241.03	$241.05	$241.00
Purchase #5	$75.81	3.107%	$78.1654	$78.17	$78.15	$78.20
Purchase #6	$22.50	8.686%	$24.4544	$24.45	$24.45	$24.50
Purchase #7	$20.59	3.323%	$21.2742	$21.27	$21.25	$21.30
7 purchase totals =	$634.14		$682.4129	$682.41	$682.40	$682.50