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	$46.85	8.551%	$50.8561	$50.86	$50.85	$50.90
Purchase #2	$70.49	8.870%	$76.7425	$76.74	$76.75	$76.70
Purchase #3	$48.87	9.102%	$53.3181	$53.32	$53.30	$53.30
Purchase #4	$24.89	10.534%	$27.5119	$27.51	$27.50	$27.50
Purchase #5	$86.47	3.307%	$89.3296	$89.33	$89.35	$89.30
Purchase #6	$29.68	7.687%	$31.9615	$31.96	$31.95	$32.00
Purchase #7	$213.95	5.379%	$225.4584	$225.46	$225.45	$225.50
7 purchase totals =	$521.20		$555.1781	$555.18	$555.15	$555.20