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	$46.64	11.484%	$51.9961	$52.00	$52.00	$52.00
Purchase #2	$88.68	10.709%	$98.1767	$98.18	$98.20	$98.20
Purchase #3	$134.44	7.506%	$144.5311	$144.53	$144.55	$144.50
Purchase #4	$137.50	4.628%	$143.8635	$143.86	$143.85	$143.90
Purchase #5	$157.51	13.534%	$178.8274	$178.83	$178.85	$178.80
Purchase #6	$69.98	3.775%	$72.6217	$72.62	$72.60	$72.60
Purchase #7	$185.72	12.674%	$209.2582	$209.26	$209.25	$209.30
7 purchase totals =	$820.47		$899.2747	$899.28	$899.30	$899.30