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	$72.47	4.196%	$75.5108	$75.51	$75.50	$75.50
Purchase #2	$123.44	3.382%	$127.6147	$127.61	$127.60	$127.60
Purchase #3	$94.25	9.727%	$103.4177	$103.42	$103.40	$103.40
Purchase #4	$50.46	12.223%	$56.6277	$56.63	$56.65	$56.60
Purchase #5	$235.26	13.872%	$267.8953	$267.90	$267.90	$267.90
Purchase #6	$249.48	3.153%	$257.3461	$257.35	$257.35	$257.30
Purchase #7	$47.71	4.589%	$49.8994	$49.90	$49.90	$49.90
7 purchase totals =	$873.07		$938.3117	$938.32	$938.30	$938.20