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	$128.81	12.396%	$144.7773	$144.78	$144.80	$144.80
Purchase #2	$230.51	3.276%	$238.0615	$238.06	$238.05	$238.10
Purchase #3	$119.48	9.866%	$131.2679	$131.27	$131.25	$131.30
Purchase #4	$183.87	12.216%	$206.3316	$206.33	$206.35	$206.30
Purchase #5	$136.43	6.561%	$145.3812	$145.38	$145.40	$145.40
Purchase #6	$164.31	13.131%	$185.8855	$185.89	$185.90	$185.90
Purchase #7	$92.53	8.237%	$100.1517	$100.15	$100.15	$100.20
7 purchase totals =	$1,055.94		$1,151.8567	$1,151.86	$1,151.90	$1,152.00