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	$74.48	7.158%	$79.8113	$79.81	$79.80	$79.80
Purchase #2	$54.78	10.307%	$60.4262	$60.43	$60.45	$60.40
Purchase #3	$159.40	13.472%	$180.8744	$180.87	$180.85	$180.90
Purchase #4	$132.26	9.118%	$144.3195	$144.32	$144.30	$144.30
Purchase #5	$174.31	12.785%	$196.5955	$196.60	$196.60	$196.60
Purchase #6	$12.71	13.776%	$14.4609	$14.46	$14.45	$14.50
Purchase #7	$47.82	9.488%	$52.3572	$52.36	$52.35	$52.40
7 purchase totals =	$655.76		$728.8450	$728.85	$728.80	$728.90