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	$31.78	9.607%	$34.8331	$34.83	$34.85	$34.80
Purchase #2	$51.67	3.394%	$53.4237	$53.42	$53.40	$53.40
Purchase #3	$43.97	4.826%	$46.092	$46.09	$46.10	$46.10
Purchase #4	$65.52	10.349%	$72.3007	$72.30	$72.30	$72.30
Purchase #5	$94.96	9.492%	$103.9736	$103.97	$103.95	$104.00
Purchase #6	$152.78	8.231%	$165.3553	$165.36	$165.35	$165.40
Purchase #7	$58.51	12.687%	$65.9332	$65.93	$65.95	$65.90
7 purchase totals =	$499.19		$541.9116	$541.90	$541.90	$541.90