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	$142.42	5.605%	$150.4026	$150.40	$150.40	$150.40
Purchase #2	$46.61	12.163%	$52.2792	$52.28	$52.30	$52.30
Purchase #3	$18.45	9.114%	$20.1315	$20.13	$20.15	$20.10
Purchase #4	$90.60	5.160%	$95.275	$95.28	$95.30	$95.30
Purchase #5	$163.98	12.346%	$184.225	$184.23	$184.25	$184.20
Purchase #6	$221.28	9.504%	$242.3105	$242.31	$242.30	$242.30
Purchase #7	$216.76	6.835%	$231.5755	$231.58	$231.60	$231.60
7 purchase totals =	$900.10		$976.1993	$976.21	$976.30	$976.20