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	$118.85	4.188%	$123.8274	$123.83	$123.85	$123.80
Purchase #2	$199.65	13.868%	$227.3375	$227.34	$227.35	$227.30
Purchase #3	$114.96	11.543%	$128.2298	$128.23	$128.25	$128.20
Purchase #4	$32.69	13.533%	$37.1139	$37.11	$37.10	$37.10
Purchase #5	$63.43	9.827%	$69.6633	$69.66	$69.65	$69.70
Purchase #6	$140.90	5.655%	$148.8679	$148.87	$148.85	$148.90
Purchase #7	$230.30	4.494%	$240.6497	$240.65	$240.65	$240.60
7 purchase totals =	$900.78		$975.6895	$975.69	$975.70	$975.60