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	$177.94	4.134%	$185.296	$185.30	$185.30	$185.30
Purchase #2	$226.85	13.786%	$258.1235	$258.12	$258.10	$258.10
Purchase #3	$221.95	11.691%	$247.8982	$247.90	$247.90	$247.90
Purchase #4	$68.25	5.755%	$72.1778	$72.18	$72.20	$72.20
Purchase #5	$225.62	12.340%	$253.4615	$253.46	$253.45	$253.50
Purchase #6	$178.50	9.848%	$196.0787	$196.08	$196.10	$196.10
Purchase #7	$69.56	12.537%	$78.2807	$78.28	$78.30	$78.30
7 purchase totals =	$1,168.67		$1,291.3164	$1,291.32	$1,291.35	$1,291.40