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	$23.64	4.753%	$24.7636	$24.76	$24.75	$24.80
Purchase #2	$239.59	13.694%	$272.3995	$272.40	$272.40	$272.40
Purchase #3	$82.60	3.363%	$85.3778	$85.38	$85.40	$85.40
Purchase #4	$163.27	4.839%	$171.1706	$171.17	$171.15	$171.20
Purchase #5	$100.87	7.616%	$108.5523	$108.55	$108.55	$108.60
Purchase #6	$86.79	4.306%	$90.5272	$90.53	$90.55	$90.50
Purchase #7	$33.47	11.357%	$37.2712	$37.27	$37.25	$37.30
7 purchase totals =	$730.23		$790.0622	$790.06	$790.05	$790.20