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	$141.74	10.857%	$157.1287	$157.13	$157.15	$157.10
Purchase #2	$17.35	4.199%	$18.0785	$18.08	$18.10	$18.10
Purchase #3	$141.83	8.241%	$153.5182	$153.52	$153.50	$153.50
Purchase #4	$57.41	10.408%	$63.3852	$63.39	$63.40	$63.40
Purchase #5	$37.59	12.577%	$42.3177	$42.32	$42.30	$42.30
Purchase #6	$139.59	3.860%	$144.9782	$144.98	$145.00	$145.00
Purchase #7	$204.32	6.856%	$218.3282	$218.33	$218.35	$218.30
7 purchase totals =	$739.83		$797.7347	$797.75	$797.80	$797.70