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	$46.42	12.698%	$52.3144	$52.31	$52.30	$52.30
Purchase #2	$239.50	7.439%	$257.3164	$257.32	$257.30	$257.30
Purchase #3	$92.33	12.169%	$103.5656	$103.57	$103.55	$103.60
Purchase #4	$102.54	7.627%	$110.3607	$110.36	$110.35	$110.40
Purchase #5	$59.85	13.324%	$67.8244	$67.82	$67.80	$67.80
Purchase #6	$250.38	11.795%	$279.9123	$279.91	$279.90	$279.90
Purchase #7	$120.95	4.668%	$126.5959	$126.60	$126.60	$126.60
7 purchase totals =	$911.97		$997.8897	$997.89	$997.80	$997.90