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	$171.77	8.550%	$186.4563	$186.46	$186.45	$186.50
Purchase #2	$210.61	11.588%	$235.0155	$235.02	$235.00	$235.00
Purchase #3	$95.71	9.710%	$105.0034	$105.00	$105.00	$105.00
Purchase #4	$175.49	4.140%	$182.7553	$182.76	$182.75	$182.80
Purchase #5	$116.70	8.798%	$126.9673	$126.97	$126.95	$127.00
Purchase #6	$55.92	5.834%	$59.1824	$59.18	$59.20	$59.20
Purchase #7	$76.39	9.278%	$83.4775	$83.48	$83.50	$83.50
7 purchase totals =	$902.59		$978.8577	$978.87	$978.85	$979.00