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	$35.90	7.507%	$38.595	$38.60	$38.60	$38.60
Purchase #2	$192.36	3.326%	$198.7579	$198.76	$198.75	$198.80
Purchase #3	$100.70	13.587%	$114.3821	$114.38	$114.40	$114.40
Purchase #4	$143.66	6.458%	$152.9376	$152.94	$152.95	$152.90
Purchase #5	$164.72	11.856%	$184.2492	$184.25	$184.25	$184.20
Purchase #6	$42.83	4.301%	$44.6721	$44.67	$44.65	$44.70
Purchase #7	$229.43	6.627%	$244.6343	$244.63	$244.65	$244.60
7 purchase totals =	$909.60		$978.2282	$978.23	$978.25	$978.20