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	$239.39	13.866%	$272.5838	$272.58	$272.60	$272.60
Purchase #2	$31.51	11.501%	$35.134	$35.13	$35.15	$35.10
Purchase #3	$79.71	12.377%	$89.5757	$89.58	$89.60	$89.60
Purchase #4	$163.33	13.798%	$185.8663	$185.87	$185.85	$185.90
Purchase #5	$241.59	11.456%	$269.2666	$269.27	$269.25	$269.30
Purchase #6	$41.78	9.645%	$45.8097	$45.81	$45.80	$45.80
Purchase #7	$70.98	12.587%	$79.9143	$79.91	$79.90	$79.90
7 purchase totals =	$868.29		$978.1504	$978.15	$978.15	$978.20