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	$249.50	10.578%	$275.8921	$275.89	$275.90	$275.90
Purchase #2	$5.67	13.659%	$6.4445	$6.44	$6.45	$6.40
Purchase #3	$188.77	13.439%	$214.1388	$214.14	$214.15	$214.10
Purchase #4	$100.51	3.285%	$103.8118	$103.81	$103.80	$103.80
Purchase #5	$174.52	6.446%	$185.7696	$185.77	$185.75	$185.80
Purchase #6	$237.62	8.134%	$256.948	$256.95	$256.95	$256.90
Purchase #7	$83.90	7.570%	$90.2512	$90.25	$90.25	$90.30
7 purchase totals =	$1,040.49		$1,133.2560	$1,133.25	$1,133.25	$1,133.20