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	$121.44	5.308%	$127.886	$127.89	$127.90	$127.90
Purchase #2	$158.59	11.754%	$177.2307	$177.23	$177.25	$177.20
Purchase #3	$166.88	4.589%	$174.5381	$174.54	$174.55	$174.50
Purchase #4	$132.45	3.520%	$137.1122	$137.11	$137.10	$137.10
Purchase #5	$231.55	5.869%	$245.1397	$245.14	$245.15	$245.10
Purchase #6	$104.25	5.368%	$109.8461	$109.85	$109.85	$109.80
Purchase #7	$230.93	11.546%	$257.5932	$257.59	$257.60	$257.60
7 purchase totals =	$1,146.09		$1,229.3460	$1,229.35	$1,229.40	$1,229.20