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	$57.69	5.560%	$60.8976	$60.90	$60.90	$60.90
Purchase #2	$127.66	9.558%	$139.8617	$139.86	$139.85	$139.90
Purchase #3	$11.81	12.144%	$13.2442	$13.24	$13.25	$13.20
Purchase #4	$123.26	5.873%	$130.4991	$130.50	$130.50	$130.50
Purchase #5	$154.27	9.135%	$168.3626	$168.36	$168.35	$168.40
Purchase #6	$113.85	11.619%	$127.0782	$127.08	$127.10	$127.10
Purchase #7	$39.78	5.524%	$41.9774	$41.98	$42.00	$42.00
7 purchase totals =	$628.32		$681.9208	$681.92	$681.95	$682.00