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	$49.61	3.839%	$51.5145	$51.51	$51.50	$51.50
Purchase #2	$5.86	9.293%	$6.4046	$6.40	$6.40	$6.40
Purchase #3	$86.31	8.792%	$93.8984	$93.90	$93.90	$93.90
Purchase #4	$128.88	10.278%	$142.1263	$142.13	$142.15	$142.10
Purchase #5	$195.86	5.476%	$206.5853	$206.59	$206.60	$206.60
Purchase #6	$119.64	3.181%	$123.4457	$123.45	$123.45	$123.40
Purchase #7	$217.27	4.832%	$227.7685	$227.77	$227.75	$227.80
7 purchase totals =	$803.43		$851.7433	$851.75	$851.75	$851.70