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	$126.81	11.583%	$141.4984	$141.50	$141.50	$141.50
Purchase #2	$78.38	6.482%	$83.4606	$83.46	$83.45	$83.50
Purchase #3	$244.48	11.673%	$273.0182	$273.02	$273.00	$273.00
Purchase #4	$171.91	10.448%	$189.8712	$189.87	$189.85	$189.90
Purchase #5	$44.88	4.350%	$46.8323	$46.83	$46.85	$46.80
Purchase #6	$242.53	3.350%	$250.6548	$250.65	$250.65	$250.70
Purchase #7	$140.34	5.768%	$148.4348	$148.43	$148.45	$148.40
7 purchase totals =	$1,049.33		$1,133.7703	$1,133.76	$1,133.75	$1,133.80