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	$242.84	3.314%	$250.8877	$250.89	$250.90	$250.90
Purchase #2	$223.82	3.434%	$231.506	$231.51	$231.50	$231.50
Purchase #3	$19.89	8.556%	$21.5918	$21.59	$21.60	$21.60
Purchase #4	$153.44	9.159%	$167.4936	$167.49	$167.50	$167.50
Purchase #5	$73.32	4.810%	$76.8467	$76.85	$76.85	$76.80
Purchase #6	$171.67	7.331%	$184.2551	$184.26	$184.25	$184.30
Purchase #7	$208.50	6.815%	$222.7093	$222.71	$222.70	$222.70
7 purchase totals =	$1,093.48		$1,155.2902	$1,155.30	$1,155.30	$1,155.30