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	$225.39	6.657%	$240.3942	$240.39	$240.40	$240.40
Purchase #2	$49.91	13.169%	$56.4826	$56.48	$56.50	$56.50
Purchase #3	$64.55	12.381%	$72.5419	$72.54	$72.55	$72.50
Purchase #4	$140.87	6.784%	$150.4266	$150.43	$150.45	$150.40
Purchase #5	$122.28	5.443%	$128.9357	$128.94	$128.95	$128.90
Purchase #6	$28.38	12.674%	$31.9769	$31.98	$32.00	$32.00
Purchase #7	$157.57	13.656%	$179.0878	$179.09	$179.10	$179.10
7 purchase totals =	$788.95		$859.8457	$859.85	$859.95	$859.80