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	$152.27	4.579%	$159.2424	$159.24	$159.25	$159.20
Purchase #2	$218.56	12.406%	$245.6746	$245.67	$245.65	$245.70
Purchase #3	$195.66	13.270%	$221.6241	$221.62	$221.60	$221.60
Purchase #4	$77.47	6.632%	$82.6078	$82.61	$82.60	$82.60
Purchase #5	$183.90	8.117%	$198.8272	$198.83	$198.85	$198.80
Purchase #6	$90.94	9.356%	$99.4483	$99.45	$99.45	$99.40
Purchase #7	$217.51	5.320%	$229.0815	$229.08	$229.10	$229.10
7 purchase totals =	$1,136.31		$1,236.5059	$1,236.50	$1,236.50	$1,236.40