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	$73.93	6.106%	$78.4442	$78.44	$78.45	$78.40
Purchase #2	$35.97	10.703%	$39.8199	$39.82	$39.80	$39.80
Purchase #3	$138.44	9.779%	$151.978	$151.98	$152.00	$152.00
Purchase #4	$180.43	10.288%	$198.9926	$198.99	$199.00	$199.00
Purchase #5	$233.86	7.169%	$250.6254	$250.63	$250.65	$250.60
Purchase #6	$142.55	13.835%	$162.2718	$162.27	$162.25	$162.30
Purchase #7	$103.38	8.795%	$112.4723	$112.47	$112.45	$112.50
7 purchase totals =	$908.56		$994.6042	$994.60	$994.60	$994.60