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	$185.51	10.709%	$205.3763	$205.38	$205.40	$205.40
Purchase #2	$159.37	7.308%	$171.0168	$171.02	$171.00	$171.00
Purchase #3	$142.85	13.130%	$161.6062	$161.61	$161.60	$161.60
Purchase #4	$48.57	8.428%	$52.6635	$52.66	$52.65	$52.70
Purchase #5	$120.61	8.622%	$131.009	$131.01	$131.00	$131.00
Purchase #6	$41.69	5.360%	$43.9246	$43.92	$43.90	$43.90
Purchase #7	$21.75	9.670%	$23.8532	$23.85	$23.85	$23.90
7 purchase totals =	$720.35		$789.4496	$789.45	$789.40	$789.50