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	$80.60	11.168%	$89.6014	$89.60	$89.60	$89.60
Purchase #2	$178.81	10.688%	$197.9212	$197.92	$197.90	$197.90
Purchase #3	$36.35	11.829%	$40.6498	$40.65	$40.65	$40.60
Purchase #4	$14.44	13.507%	$16.3904	$16.39	$16.40	$16.40
Purchase #5	$98.47	13.498%	$111.7615	$111.76	$111.75	$111.80
Purchase #6	$135.94	10.693%	$150.4761	$150.48	$150.50	$150.50
Purchase #7	$78.42	9.526%	$85.8903	$85.89	$85.90	$85.90
7 purchase totals =	$623.03		$692.6907	$692.69	$692.70	$692.70