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	$248.37	8.787%	$270.1943	$270.19	$270.20	$270.20
Purchase #2	$99.97	9.320%	$109.2872	$109.29	$109.30	$109.30
Purchase #3	$16.61	3.356%	$17.1674	$17.17	$17.15	$17.20
Purchase #4	$37.51	9.211%	$40.965	$40.97	$40.95	$41.00
Purchase #5	$129.85	6.728%	$138.5863	$138.59	$138.60	$138.60
Purchase #6	$38.70	4.758%	$40.5413	$40.54	$40.55	$40.50
Purchase #7	$68.39	6.380%	$72.7533	$72.75	$72.75	$72.80
7 purchase totals =	$639.40		$689.4948	$689.50	$689.50	$689.60