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	$37.35	13.724%	$42.4759	$42.48	$42.50	$42.50
Purchase #2	$72.37	13.505%	$82.1436	$82.14	$82.15	$82.10
Purchase #3	$113.63	8.472%	$123.2567	$123.26	$123.25	$123.30
Purchase #4	$160.61	9.221%	$175.4198	$175.42	$175.40	$175.40
Purchase #5	$201.45	5.122%	$211.7683	$211.77	$211.75	$211.80
Purchase #6	$45.70	3.679%	$47.3813	$47.38	$47.40	$47.40
Purchase #7	$182.99	12.296%	$205.4905	$205.49	$205.50	$205.50
7 purchase totals =	$814.10		$887.9361	$887.94	$887.95	$888.00