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	$61.77	13.559%	$70.1454	$70.15	$70.15	$70.10
Purchase #2	$143.93	4.832%	$150.8847	$150.88	$150.90	$150.90
Purchase #3	$55.38	11.662%	$61.8384	$61.84	$61.85	$61.80
Purchase #4	$66.98	13.187%	$75.8127	$75.81	$75.80	$75.80
Purchase #5	$131.92	11.115%	$146.5829	$146.58	$146.60	$146.60
Purchase #6	$112.98	4.537%	$118.1059	$118.11	$118.10	$118.10
Purchase #7	$196.94	8.390%	$213.4633	$213.46	$213.45	$213.50
7 purchase totals =	$769.90		$836.8333	$836.83	$836.85	$836.80