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	$70.95	10.698%	$78.5402	$78.54	$78.55	$78.50
Purchase #2	$192.79	13.253%	$218.3405	$218.34	$218.35	$218.30
Purchase #3	$72.33	10.842%	$80.172	$80.17	$80.15	$80.20
Purchase #4	$240.70	13.574%	$273.3726	$273.37	$273.35	$273.40
Purchase #5	$44.47	9.801%	$48.8285	$48.83	$48.85	$48.80
Purchase #6	$29.79	4.291%	$31.0683	$31.07	$31.05	$31.10
Purchase #7	$50.60	11.805%	$56.5733	$56.57	$56.55	$56.60
7 purchase totals =	$701.63		$786.8954	$786.89	$786.85	$786.90