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	$54.53	5.441%	$57.497	$57.50	$57.50	$57.50
Purchase #2	$155.75	6.624%	$166.0669	$166.07	$166.05	$166.10
Purchase #3	$150.41	12.110%	$168.6247	$168.62	$168.60	$168.60
Purchase #4	$246.55	13.396%	$279.5778	$279.58	$279.60	$279.60
Purchase #5	$36.41	11.727%	$40.6798	$40.68	$40.70	$40.70
Purchase #6	$80.35	6.198%	$85.3301	$85.33	$85.35	$85.30
Purchase #7	$206.70	5.558%	$218.1884	$218.19	$218.20	$218.20
7 purchase totals =	$930.70		$1,015.9647	$1,015.97	$1,016.00	$1,016.00