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	$22.46	9.301%	$24.549	$24.55	$24.55	$24.50
Purchase #2	$147.57	13.770%	$167.8904	$167.89	$167.90	$167.90
Purchase #3	$242.35	5.241%	$255.0516	$255.05	$255.05	$255.10
Purchase #4	$158.88	13.452%	$180.2525	$180.25	$180.25	$180.30
Purchase #5	$110.52	3.244%	$114.1053	$114.11	$114.10	$114.10
Purchase #6	$18.77	3.306%	$19.3905	$19.39	$19.40	$19.40
Purchase #7	$69.49	13.225%	$78.6801	$78.68	$78.70	$78.70
7 purchase totals =	$770.04		$839.9194	$839.92	$839.95	$840.00