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	$91.48	13.867%	$104.1655	$104.17	$104.15	$104.20
Purchase #2	$37.65	13.562%	$42.7561	$42.76	$42.75	$42.80
Purchase #3	$248.36	12.754%	$280.0358	$280.04	$280.05	$280.00
Purchase #4	$231.51	13.372%	$262.4675	$262.47	$262.45	$262.50
Purchase #5	$214.88	4.431%	$224.4013	$224.40	$224.40	$224.40
Purchase #6	$189.66	3.658%	$196.5978	$196.60	$196.60	$196.60
Purchase #7	$21.86	6.439%	$23.2676	$23.27	$23.25	$23.30
7 purchase totals =	$1,035.40		$1,133.6916	$1,133.71	$1,133.65	$1,133.80