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	$32.51	5.442%	$34.2792	$34.28	$34.30	$34.30
Purchase #2	$150.58	9.270%	$164.5388	$164.54	$164.55	$164.50
Purchase #3	$135.73	4.338%	$141.618	$141.62	$141.60	$141.60
Purchase #4	$154.29	7.294%	$165.5439	$165.54	$165.55	$165.50
Purchase #5	$6.77	10.225%	$7.4622	$7.46	$7.45	$7.50
Purchase #6	$244.39	9.849%	$268.46	$268.46	$268.45	$268.50
Purchase #7	$108.59	8.228%	$117.5248	$117.52	$117.50	$117.50
7 purchase totals =	$832.86		$899.4269	$899.42	$899.40	$899.40