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	$112.74	9.362%	$123.2947	$123.29	$123.30	$123.30
Purchase #2	$175.26	4.146%	$182.5263	$182.53	$182.55	$182.50
Purchase #3	$124.70	5.794%	$131.9251	$131.93	$131.95	$131.90
Purchase #4	$113.81	3.721%	$118.0449	$118.04	$118.05	$118.00
Purchase #5	$61.61	7.850%	$66.4464	$66.45	$66.45	$66.40
Purchase #6	$181.59	8.339%	$196.7328	$196.73	$196.75	$196.70
Purchase #7	$85.73	9.196%	$93.6137	$93.61	$93.60	$93.60
7 purchase totals =	$855.44		$912.5839	$912.58	$912.65	$912.40