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	$35.29	9.593%	$38.6754	$38.68	$38.70	$38.70
Purchase #2	$148.79	12.266%	$167.0406	$167.04	$167.05	$167.00
Purchase #3	$59.89	13.393%	$67.9111	$67.91	$67.90	$67.90
Purchase #4	$29.66	6.602%	$31.6182	$31.62	$31.60	$31.60
Purchase #5	$185.66	10.804%	$205.7187	$205.72	$205.70	$205.70
Purchase #6	$108.27	4.137%	$112.7491	$112.75	$112.75	$112.70
Purchase #7	$29.42	10.759%	$32.5853	$32.59	$32.60	$32.60
7 purchase totals =	$596.98		$656.2984	$656.31	$656.30	$656.20