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	$18.89	10.296%	$20.8349	$20.83	$20.85	$20.80
Purchase #2	$35.27	4.703%	$36.9287	$36.93	$36.95	$36.90
Purchase #3	$132.30	7.757%	$142.5625	$142.56	$142.55	$142.60
Purchase #4	$26.27	5.185%	$27.6321	$27.63	$27.65	$27.60
Purchase #5	$209.59	12.341%	$235.4555	$235.46	$235.45	$235.50
Purchase #6	$31.92	5.319%	$33.6178	$33.62	$33.60	$33.60
Purchase #7	$209.88	7.279%	$225.1572	$225.16	$225.15	$225.20
7 purchase totals =	$664.12		$722.1887	$722.19	$722.20	$722.20