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	$217.70	10.673%	$240.9351	$240.94	$240.95	$240.90
Purchase #2	$80.55	9.702%	$88.365	$88.37	$88.35	$88.40
Purchase #3	$91.90	12.814%	$103.6761	$103.68	$103.70	$103.70
Purchase #4	$164.86	5.195%	$173.4245	$173.42	$173.40	$173.40
Purchase #5	$104.75	7.410%	$112.512	$112.51	$112.50	$112.50
Purchase #6	$11.39	7.872%	$12.2866	$12.29	$12.30	$12.30
Purchase #7	$76.25	3.478%	$78.902	$78.90	$78.90	$78.90
7 purchase totals =	$747.40		$810.1013	$810.11	$810.10	$810.10