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	$99.52	3.873%	$103.3744	$103.37	$103.35	$103.40
Purchase #2	$70.73	12.342%	$79.4595	$79.46	$79.45	$79.50
Purchase #3	$42.82	11.752%	$47.8522	$47.85	$47.85	$47.90
Purchase #4	$9.51	13.208%	$10.7661	$10.77	$10.75	$10.80
Purchase #5	$126.86	8.215%	$137.2815	$137.28	$137.30	$137.30
Purchase #6	$29.67	5.577%	$31.3247	$31.32	$31.30	$31.30
Purchase #7	$130.42	11.577%	$145.5187	$145.52	$145.50	$145.50
7 purchase totals =	$509.53		$555.5771	$555.57	$555.50	$555.70