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	$110.70	10.705%	$122.5504	$122.55	$122.55	$122.60
Purchase #2	$44.87	7.106%	$48.0585	$48.06	$48.05	$48.10
Purchase #3	$102.69	11.224%	$114.2159	$114.22	$114.20	$114.20
Purchase #4	$130.69	12.168%	$146.5924	$146.59	$146.60	$146.60
Purchase #5	$196.38	13.352%	$222.6007	$222.60	$222.60	$222.60
Purchase #6	$187.50	11.503%	$209.0681	$209.07	$209.05	$209.10
Purchase #7	$38.36	5.304%	$40.3946	$40.39	$40.40	$40.40
7 purchase totals =	$811.19		$903.4806	$903.48	$903.45	$903.60