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	$128.61	12.290%	$144.4162	$144.42	$144.40	$144.40
Purchase #2	$30.37	9.384%	$33.2199	$33.22	$33.20	$33.20
Purchase #3	$145.65	13.629%	$165.5006	$165.50	$165.50	$165.50
Purchase #4	$61.38	8.511%	$66.6041	$66.60	$66.60	$66.60
Purchase #5	$62.64	12.297%	$70.3428	$70.34	$70.35	$70.30
Purchase #6	$121.42	7.509%	$130.5374	$130.54	$130.55	$130.50
Purchase #7	$226.28	6.756%	$241.5675	$241.57	$241.55	$241.60
7 purchase totals =	$776.35		$852.1885	$852.19	$852.15	$852.10