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	$14.64	7.794%	$15.781	$15.78	$15.80	$15.80
Purchase #2	$132.32	13.853%	$150.6503	$150.65	$150.65	$150.70
Purchase #3	$38.50	13.762%	$43.7984	$43.80	$43.80	$43.80
Purchase #4	$238.89	6.547%	$254.5301	$254.53	$254.55	$254.50
Purchase #5	$175.79	13.553%	$199.6148	$199.61	$199.60	$199.60
Purchase #6	$129.81	9.820%	$142.5573	$142.56	$142.55	$142.60
Purchase #7	$69.83	11.531%	$77.8821	$77.88	$77.90	$77.90
7 purchase totals =	$799.78		$884.8140	$884.81	$884.85	$884.90