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	$122.29	7.380%	$131.315	$131.32	$131.30	$131.30
Purchase #2	$84.75	12.713%	$95.5243	$95.52	$95.50	$95.50
Purchase #3	$139.62	13.443%	$158.3891	$158.39	$158.40	$158.40
Purchase #4	$26.33	4.332%	$27.4706	$27.47	$27.45	$27.50
Purchase #5	$44.60	5.592%	$47.094	$47.09	$47.10	$47.10
Purchase #6	$101.37	8.833%	$110.324	$110.32	$110.30	$110.30
Purchase #7	$84.72	6.840%	$90.5148	$90.51	$90.50	$90.50
7 purchase totals =	$603.68		$660.6318	$660.62	$660.55	$660.60