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	$79.27	13.650%	$90.0904	$90.09	$90.10	$90.10
Purchase #2	$80.90	11.787%	$90.4357	$90.44	$90.45	$90.40
Purchase #3	$130.68	12.551%	$147.0816	$147.08	$147.10	$147.10
Purchase #4	$141.92	4.674%	$148.5533	$148.55	$148.55	$148.60
Purchase #5	$51.75	10.287%	$57.0735	$57.07	$57.05	$57.10
Purchase #6	$108.47	7.860%	$116.9957	$117.00	$117.00	$117.00
Purchase #7	$218.42	13.617%	$248.1623	$248.16	$248.15	$248.20
7 purchase totals =	$811.41		$898.3925	$898.39	$898.40	$898.50