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	$10.53	12.638%	$11.8608	$11.86	$11.85	$11.90
Purchase #2	$96.33	7.587%	$103.6386	$103.64	$103.65	$103.60
Purchase #3	$100.40	4.561%	$104.9792	$104.98	$105.00	$105.00
Purchase #4	$184.33	7.633%	$198.3999	$198.40	$198.40	$198.40
Purchase #5	$190.91	12.425%	$214.6306	$214.63	$214.65	$214.60
Purchase #6	$88.43	3.442%	$91.4738	$91.47	$91.45	$91.50
Purchase #7	$241.37	5.160%	$253.8247	$253.82	$253.80	$253.80
7 purchase totals =	$912.30		$978.8076	$978.80	$978.80	$978.80