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	$90.29	11.386%	$100.5704	$100.57	$100.55	$100.60
Purchase #2	$199.65	7.404%	$214.4321	$214.43	$214.45	$214.40
Purchase #3	$100.29	12.672%	$112.9987	$113.00	$113.00	$113.00
Purchase #4	$96.66	8.149%	$104.5368	$104.54	$104.55	$104.50
Purchase #5	$142.89	5.233%	$150.3674	$150.37	$150.35	$150.40
Purchase #6	$238.98	4.655%	$250.1045	$250.10	$250.10	$250.10
Purchase #7	$136.47	10.731%	$151.1146	$151.11	$151.10	$151.10
7 purchase totals =	$1,005.23		$1,084.1245	$1,084.12	$1,084.10	$1,084.10