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	$32.99	13.618%	$37.4826	$37.48	$37.50	$37.50
Purchase #2	$92.84	3.479%	$96.0699	$96.07	$96.05	$96.10
Purchase #3	$89.50	11.112%	$99.4452	$99.45	$99.45	$99.40
Purchase #4	$35.46	9.508%	$38.8315	$38.83	$38.85	$38.80
Purchase #5	$138.56	10.665%	$153.3374	$153.34	$153.35	$153.30
Purchase #6	$120.38	10.297%	$132.7755	$132.78	$132.80	$132.80
Purchase #7	$250.76	4.619%	$262.3426	$262.34	$262.35	$262.30
7 purchase totals =	$760.49		$820.2847	$820.29	$820.35	$820.20