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	$88.49	6.577%	$94.31	$94.31	$94.30	$94.30
Purchase #2	$54.89	3.133%	$56.6097	$56.61	$56.60	$56.60
Purchase #3	$74.86	12.307%	$84.073	$84.07	$84.05	$84.10
Purchase #4	$142.39	5.869%	$150.7469	$150.75	$150.75	$150.70
Purchase #5	$29.55	6.750%	$31.5446	$31.54	$31.55	$31.50
Purchase #6	$91.94	12.468%	$103.4031	$103.40	$103.40	$103.40
Purchase #7	$88.47	4.153%	$92.1442	$92.14	$92.15	$92.10
7 purchase totals =	$570.59		$612.8315	$612.82	$612.80	$612.70