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	$47.32	13.848%	$53.8729	$53.87	$53.85	$53.90
Purchase #2	$94.84	8.502%	$102.9033	$102.90	$102.90	$102.90
Purchase #3	$31.52	12.520%	$35.4663	$35.47	$35.45	$35.50
Purchase #4	$222.91	11.414%	$248.3529	$248.35	$248.35	$248.40
Purchase #5	$201.57	9.467%	$220.6526	$220.65	$220.65	$220.70
Purchase #6	$200.60	11.119%	$222.9047	$222.90	$222.90	$222.90
Purchase #7	$27.72	6.708%	$29.5795	$29.58	$29.60	$29.60
7 purchase totals =	$826.48		$913.7322	$913.72	$913.70	$913.90