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	$128.30	8.537%	$139.253	$139.25	$139.25	$139.30
Purchase #2	$144.64	6.844%	$154.5392	$154.54	$154.55	$154.50
Purchase #3	$230.90	7.842%	$249.0072	$249.01	$249.00	$249.00
Purchase #4	$123.43	12.726%	$139.1377	$139.14	$139.15	$139.10
Purchase #5	$150.89	11.573%	$168.3525	$168.35	$168.35	$168.40
Purchase #6	$125.50	6.425%	$133.5634	$133.56	$133.55	$133.60
Purchase #7	$15.81	13.590%	$17.9586	$17.96	$17.95	$18.00
7 purchase totals =	$919.47		$1,001.8116	$1,001.81	$1,001.80	$1,001.90