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	$92.72	7.424%	$99.6035	$99.60	$99.60	$99.60
Purchase #2	$90.88	9.854%	$99.8353	$99.84	$99.85	$99.80
Purchase #3	$27.50	11.298%	$30.607	$30.61	$30.60	$30.60
Purchase #4	$49.97	4.695%	$52.3161	$52.32	$52.30	$52.30
Purchase #5	$132.38	9.858%	$145.43	$145.43	$145.45	$145.40
Purchase #6	$91.67	12.351%	$102.9922	$102.99	$103.00	$103.00
Purchase #7	$119.73	8.241%	$129.5969	$129.60	$129.60	$129.60
7 purchase totals =	$604.85		$660.3810	$660.39	$660.40	$660.30