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	$51.49	8.376%	$55.8028	$55.80	$55.80	$55.80
Purchase #2	$132.47	13.821%	$150.7787	$150.78	$150.80	$150.80
Purchase #3	$33.82	7.865%	$36.4799	$36.48	$36.50	$36.50
Purchase #4	$127.40	3.161%	$131.4271	$131.43	$131.45	$131.40
Purchase #5	$227.34	6.715%	$242.6059	$242.61	$242.60	$242.60
Purchase #6	$196.80	12.605%	$221.6066	$221.61	$221.60	$221.60
Purchase #7	$23.95	13.306%	$27.1368	$27.14	$27.15	$27.10
7 purchase totals =	$793.27		$865.8378	$865.85	$865.90	$865.80