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	$239.54	5.555%	$252.8464	$252.85	$252.85	$252.80
Purchase #2	$121.65	8.245%	$131.68	$131.68	$131.70	$131.70
Purchase #3	$37.30	11.358%	$41.5365	$41.54	$41.55	$41.50
Purchase #4	$56.33	7.872%	$60.7643	$60.76	$60.75	$60.80
Purchase #5	$50.52	11.493%	$56.3263	$56.33	$56.35	$56.30
Purchase #6	$54.30	9.506%	$59.4618	$59.46	$59.45	$59.50
Purchase #7	$219.81	3.508%	$227.5209	$227.52	$227.50	$227.50
7 purchase totals =	$779.45		$830.1362	$830.14	$830.15	$830.10