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	$167.78	11.802%	$187.5814	$187.58	$187.60	$187.60
Purchase #2	$242.98	12.733%	$273.9186	$273.92	$273.90	$273.90
Purchase #3	$70.85	12.316%	$79.5759	$79.58	$79.60	$79.60
Purchase #4	$94.26	12.129%	$105.6928	$105.69	$105.70	$105.70
Purchase #5	$249.84	4.318%	$260.6281	$260.63	$260.65	$260.60
Purchase #6	$52.90	7.323%	$56.7739	$56.77	$56.75	$56.80
Purchase #7	$130.43	4.472%	$136.2628	$136.26	$136.25	$136.30
7 purchase totals =	$1,009.04		$1,100.4335	$1,100.43	$1,100.45	$1,100.50