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	$83.38	8.696%	$90.6307	$90.63	$90.65	$90.60
Purchase #2	$18.43	12.333%	$20.703	$20.70	$20.70	$20.70
Purchase #3	$107.79	13.548%	$122.3934	$122.39	$122.40	$122.40
Purchase #4	$33.41	12.343%	$37.5338	$37.53	$37.55	$37.50
Purchase #5	$186.94	11.726%	$208.8606	$208.86	$208.85	$208.90
Purchase #6	$19.48	6.828%	$20.8101	$20.81	$20.80	$20.80
Purchase #7	$43.36	11.627%	$48.4015	$48.40	$48.40	$48.40
7 purchase totals =	$492.79		$549.3331	$549.32	$549.35	$549.30