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	$20.93	10.162%	$23.0569	$23.06	$23.05	$23.10
Purchase #2	$108.46	3.441%	$112.1921	$112.19	$112.20	$112.20
Purchase #3	$104.44	6.761%	$111.5012	$111.50	$111.50	$111.50
Purchase #4	$185.52	3.413%	$191.8518	$191.85	$191.85	$191.90
Purchase #5	$58.54	13.729%	$66.577	$66.58	$66.60	$66.60
Purchase #6	$147.97	13.328%	$167.6914	$167.69	$167.70	$167.70
Purchase #7	$72.44	7.108%	$77.589	$77.59	$77.60	$77.60
7 purchase totals =	$698.30		$750.4594	$750.46	$750.50	$750.60