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	$82.85	6.685%	$88.3885	$88.39	$88.40	$88.40
Purchase #2	$74.59	6.517%	$79.451	$79.45	$79.45	$79.50
Purchase #3	$221.88	11.277%	$246.9014	$246.90	$246.90	$246.90
Purchase #4	$105.50	8.554%	$114.5245	$114.52	$114.50	$114.50
Purchase #5	$78.50	4.592%	$82.1047	$82.10	$82.10	$82.10
Purchase #6	$35.96	12.636%	$40.5039	$40.50	$40.50	$40.50
Purchase #7	$165.32	6.679%	$176.3617	$176.36	$176.35	$176.40
7 purchase totals =	$764.60		$828.2357	$828.22	$828.20	$828.30