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	$105.90	6.123%	$112.3843	$112.38	$112.40	$112.40
Purchase #2	$83.59	6.488%	$89.0133	$89.01	$89.00	$89.00
Purchase #3	$126.70	8.692%	$137.7128	$137.71	$137.70	$137.70
Purchase #4	$139.30	4.285%	$145.269	$145.27	$145.25	$145.30
Purchase #5	$40.57	3.274%	$41.8983	$41.90	$41.90	$41.90
Purchase #6	$96.36	4.741%	$100.9284	$100.93	$100.95	$100.90
Purchase #7	$51.66	7.277%	$55.4193	$55.42	$55.40	$55.40
7 purchase totals =	$644.08		$682.6254	$682.62	$682.60	$682.60