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	$89.85	4.541%	$93.9301	$93.93	$93.95	$93.90
Purchase #2	$70.51	11.307%	$78.4826	$78.48	$78.50	$78.50
Purchase #3	$230.71	8.262%	$249.7713	$249.77	$249.75	$249.80
Purchase #4	$244.45	6.523%	$260.3955	$260.40	$260.40	$260.40
Purchase #5	$125.46	9.467%	$137.3373	$137.34	$137.35	$137.30
Purchase #6	$36.98	11.779%	$41.3359	$41.34	$41.35	$41.30
Purchase #7	$35.37	8.229%	$38.2806	$38.28	$38.30	$38.30
7 purchase totals =	$833.33		$899.5333	$899.54	$899.60	$899.50