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	$158.35	8.241%	$171.3996	$171.40	$171.40	$171.40
Purchase #2	$183.25	4.697%	$191.8573	$191.86	$191.85	$191.90
Purchase #3	$237.46	7.749%	$255.8608	$255.86	$255.85	$255.90
Purchase #4	$74.48	8.199%	$80.5866	$80.59	$80.60	$80.60
Purchase #5	$133.48	5.554%	$140.8935	$140.89	$140.90	$140.90
Purchase #6	$134.78	4.450%	$140.7777	$140.78	$140.80	$140.80
Purchase #7	$123.86	3.500%	$128.1951	$128.20	$128.20	$128.20
7 purchase totals =	$1,045.66		$1,109.5706	$1,109.58	$1,109.60	$1,109.70