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	$140.63	13.373%	$159.4364	$159.44	$159.45	$159.40
Purchase #2	$139.56	9.172%	$152.3604	$152.36	$152.35	$152.40
Purchase #3	$42.25	11.446%	$47.0859	$47.09	$47.10	$47.10
Purchase #4	$141.43	11.229%	$157.3112	$157.31	$157.30	$157.30
Purchase #5	$46.40	11.299%	$51.6427	$51.64	$51.65	$51.60
Purchase #6	$48.75	6.868%	$52.0982	$52.10	$52.10	$52.10
Purchase #7	$185.58	6.103%	$196.9059	$196.91	$196.90	$196.90
7 purchase totals =	$744.60		$816.8407	$816.85	$816.85	$816.80