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	$250.97	11.590%	$280.0574	$280.06	$280.05	$280.10
Purchase #2	$202.66	6.559%	$215.9525	$215.95	$215.95	$216.00
Purchase #3	$189.67	13.799%	$215.8426	$215.84	$215.85	$215.80
Purchase #4	$62.35	5.177%	$65.5779	$65.58	$65.60	$65.60
Purchase #5	$100.33	4.573%	$104.9181	$104.92	$104.90	$104.90
Purchase #6	$73.94	6.651%	$78.8577	$78.86	$78.85	$78.90
Purchase #7	$161.99	5.140%	$170.3163	$170.32	$170.30	$170.30
7 purchase totals =	$1,041.91		$1,131.5225	$1,131.53	$1,131.50	$1,131.60