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	$179.78	11.702%	$200.8179	$200.82	$200.80	$200.80
Purchase #2	$105.37	3.109%	$108.646	$108.65	$108.65	$108.60
Purchase #3	$30.94	5.519%	$32.6476	$32.65	$32.65	$32.60
Purchase #4	$123.25	11.458%	$137.372	$137.37	$137.35	$137.40
Purchase #5	$12.38	9.348%	$13.5373	$13.54	$13.55	$13.50
Purchase #6	$104.32	12.470%	$117.3287	$117.33	$117.35	$117.30
Purchase #7	$36.65	6.443%	$39.0114	$39.01	$39.00	$39.00
7 purchase totals =	$592.69		$649.3609	$649.37	$649.35	$649.20