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	$250.57	5.607%	$264.6195	$264.62	$264.60	$264.60
Purchase #2	$192.43	12.677%	$216.8244	$216.82	$216.80	$216.80
Purchase #3	$126.48	6.651%	$134.8922	$134.89	$134.90	$134.90
Purchase #4	$132.48	7.647%	$142.6107	$142.61	$142.60	$142.60
Purchase #5	$242.90	12.699%	$273.7459	$273.75	$273.75	$273.70
Purchase #6	$105.90	3.713%	$109.8321	$109.83	$109.85	$109.80
Purchase #7	$117.70	11.554%	$131.2991	$131.30	$131.30	$131.30
7 purchase totals =	$1,168.46		$1,273.8239	$1,273.82	$1,273.80	$1,273.70