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	$64.97	9.450%	$71.1097	$71.11	$71.10	$71.10
Purchase #2	$131.39	4.176%	$136.8768	$136.88	$136.90	$136.90
Purchase #3	$102.29	5.418%	$107.8321	$107.83	$107.85	$107.80
Purchase #4	$146.48	12.476%	$164.7548	$164.75	$164.75	$164.80
Purchase #5	$37.90	12.676%	$42.7042	$42.70	$42.70	$42.70
Purchase #6	$200.72	10.462%	$221.7193	$221.72	$221.70	$221.70
Purchase #7	$221.55	11.762%	$247.6087	$247.61	$247.60	$247.60
7 purchase totals =	$905.30		$992.6056	$992.60	$992.60	$992.60