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	$51.57	10.652%	$57.0632	$57.06	$57.05	$57.10
Purchase #2	$224.66	13.791%	$255.6429	$255.64	$255.65	$255.60
Purchase #3	$211.84	11.825%	$236.8901	$236.89	$236.90	$236.90
Purchase #4	$198.79	9.382%	$217.4405	$217.44	$217.45	$217.40
Purchase #5	$52.89	12.688%	$59.6007	$59.60	$59.60	$59.60
Purchase #6	$73.56	7.198%	$78.8548	$78.85	$78.85	$78.90
Purchase #7	$5.74	12.598%	$6.4631	$6.46	$6.45	$6.50
7 purchase totals =	$819.05		$911.9553	$911.94	$911.95	$912.00