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	$67.76	13.326%	$76.7897	$76.79	$76.80	$76.80
Purchase #2	$132.94	3.431%	$137.5012	$137.50	$137.50	$137.50
Purchase #3	$157.55	4.666%	$164.9013	$164.90	$164.90	$164.90
Purchase #4	$109.38	12.487%	$123.0383	$123.04	$123.05	$123.00
Purchase #5	$189.43	5.298%	$199.466	$199.47	$199.45	$199.50
Purchase #6	$212.91	6.648%	$227.0643	$227.06	$227.05	$227.10
Purchase #7	$60.31	7.847%	$65.0425	$65.04	$65.05	$65.00
7 purchase totals =	$930.28		$993.8033	$993.80	$993.80	$993.80