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	$160.79	3.473%	$166.3742	$166.37	$166.35	$166.40
Purchase #2	$96.93	11.737%	$108.3067	$108.31	$108.30	$108.30
Purchase #3	$123.47	13.553%	$140.2039	$140.20	$140.20	$140.20
Purchase #4	$36.94	8.643%	$40.1327	$40.13	$40.15	$40.10
Purchase #5	$230.67	12.467%	$259.4276	$259.43	$259.45	$259.40
Purchase #6	$80.63	12.459%	$90.6757	$90.68	$90.70	$90.70
Purchase #7	$73.93	11.874%	$82.7084	$82.71	$82.70	$82.70
7 purchase totals =	$803.36		$887.8292	$887.83	$887.85	$887.80