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	$243.45	12.510%	$273.9056	$273.91	$273.90	$273.90
Purchase #2	$55.91	6.635%	$59.6196	$59.62	$59.60	$59.60
Purchase #3	$105.45	8.631%	$114.5514	$114.55	$114.55	$114.60
Purchase #4	$81.98	3.521%	$84.8665	$84.87	$84.85	$84.90
Purchase #5	$81.68	9.519%	$89.4551	$89.46	$89.45	$89.50
Purchase #6	$199.44	12.713%	$224.7948	$224.79	$224.80	$224.80
Purchase #7	$234.95	7.270%	$252.0309	$252.03	$252.05	$252.00
7 purchase totals =	$1,002.86		$1,099.2239	$1,099.23	$1,099.20	$1,099.30