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	$150.80	12.411%	$169.5158	$169.52	$169.50	$169.50
Purchase #2	$204.37	11.257%	$227.3759	$227.38	$227.40	$227.40
Purchase #3	$187.82	9.627%	$205.9014	$205.90	$205.90	$205.90
Purchase #4	$191.96	13.329%	$217.5463	$217.55	$217.55	$217.50
Purchase #5	$40.72	10.643%	$45.0538	$45.05	$45.05	$45.10
Purchase #6	$100.66	13.583%	$114.3326	$114.33	$114.35	$114.30
Purchase #7	$204.87	7.547%	$220.3315	$220.33	$220.35	$220.30
7 purchase totals =	$1,081.20		$1,200.0573	$1,200.06	$1,200.10	$1,200.00