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	$134.35	11.760%	$150.1496	$150.15	$150.15	$150.10
Purchase #2	$137.85	4.800%	$144.4668	$144.47	$144.45	$144.50
Purchase #3	$11.87	9.274%	$12.9708	$12.97	$12.95	$13.00
Purchase #4	$225.29	8.780%	$245.0705	$245.07	$245.05	$245.10
Purchase #5	$244.74	5.661%	$258.5947	$258.59	$258.60	$258.60
Purchase #6	$80.37	10.243%	$88.6023	$88.60	$88.60	$88.60
Purchase #7	$195.77	6.835%	$209.1509	$209.15	$209.15	$209.20
7 purchase totals =	$1,030.24		$1,109.0056	$1,109.00	$1,108.95	$1,109.10