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	$240.71	5.639%	$254.2836	$254.28	$254.30	$254.30
Purchase #2	$99.49	13.550%	$112.9709	$112.97	$112.95	$113.00
Purchase #3	$58.93	13.515%	$66.8944	$66.89	$66.90	$66.90
Purchase #4	$114.74	13.860%	$130.643	$130.64	$130.65	$130.60
Purchase #5	$50.30	13.659%	$57.1705	$57.17	$57.15	$57.20
Purchase #6	$130.46	12.363%	$146.5888	$146.59	$146.60	$146.60
Purchase #7	$237.60	10.621%	$262.8355	$262.84	$262.85	$262.80
7 purchase totals =	$932.23		$1,031.3867	$1,031.38	$1,031.40	$1,031.40