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	$230.34	4.431%	$240.5464	$240.55	$240.55	$240.50
Purchase #2	$98.71	8.240%	$106.8437	$106.84	$106.85	$106.80
Purchase #3	$144.88	5.126%	$152.3065	$152.31	$152.30	$152.30
Purchase #4	$55.66	6.747%	$59.4154	$59.42	$59.40	$59.40
Purchase #5	$64.39	3.438%	$66.6037	$66.60	$66.60	$66.60
Purchase #6	$234.42	8.225%	$253.701	$253.70	$253.70	$253.70
Purchase #7	$120.80	9.183%	$131.8931	$131.89	$131.90	$131.90
7 purchase totals =	$949.20		$1,011.3098	$1,011.31	$1,011.30	$1,011.20