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	$220.94	9.791%	$242.5722	$242.57	$242.55	$242.60
Purchase #2	$112.67	9.305%	$123.1539	$123.15	$123.15	$123.20
Purchase #3	$136.72	8.789%	$148.7363	$148.74	$148.75	$148.70
Purchase #4	$72.56	8.572%	$78.7798	$78.78	$78.80	$78.80
Purchase #5	$83.65	11.143%	$92.9711	$92.97	$92.95	$93.00
Purchase #6	$66.61	12.737%	$75.0941	$75.09	$75.10	$75.10
Purchase #7	$11.78	6.445%	$12.5392	$12.54	$12.55	$12.50
7 purchase totals =	$704.93		$773.8466	$773.84	$773.85	$773.90