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	$51.80	11.847%	$57.9367	$57.94	$57.95	$57.90
Purchase #2	$229.51	8.439%	$248.8783	$248.88	$248.90	$248.90
Purchase #3	$141.90	5.827%	$150.1685	$150.17	$150.15	$150.20
Purchase #4	$45.33	7.712%	$48.8258	$48.83	$48.85	$48.80
Purchase #5	$139.42	5.696%	$147.3614	$147.36	$147.35	$147.40
Purchase #6	$141.71	13.143%	$160.3349	$160.33	$160.35	$160.30
Purchase #7	$73.26	7.202%	$78.5362	$78.54	$78.55	$78.50
7 purchase totals =	$822.93		$892.0418	$892.05	$892.10	$892.00