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	$73.91	5.863%	$78.2433	$78.24	$78.25	$78.20
Purchase #2	$216.90	8.666%	$235.6966	$235.70	$235.70	$235.70
Purchase #3	$123.27	13.323%	$139.6933	$139.69	$139.70	$139.70
Purchase #4	$82.75	9.341%	$90.4797	$90.48	$90.50	$90.50
Purchase #5	$238.98	6.107%	$253.5745	$253.57	$253.55	$253.60
Purchase #6	$51.25	4.785%	$53.7023	$53.70	$53.70	$53.70
Purchase #7	$40.39	9.247%	$44.1249	$44.12	$44.10	$44.10
7 purchase totals =	$827.45		$895.5146	$895.50	$895.50	$895.50