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	$168.48	9.549%	$184.5682	$184.57	$184.55	$184.60
Purchase #2	$117.56	11.508%	$131.0888	$131.09	$131.10	$131.10
Purchase #3	$60.57	12.299%	$68.0195	$68.02	$68.00	$68.00
Purchase #4	$80.57	12.270%	$90.4559	$90.46	$90.45	$90.50
Purchase #5	$170.32	9.207%	$186.0014	$186.00	$186.00	$186.00
Purchase #6	$19.83	6.265%	$21.0723	$21.07	$21.05	$21.10
Purchase #7	$72.96	12.500%	$82.08	$82.08	$82.10	$82.10
7 purchase totals =	$690.29		$763.2861	$763.29	$763.25	$763.40