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	$134.73	5.758%	$142.4878	$142.49	$142.50	$142.50
Purchase #2	$48.29	8.462%	$52.3763	$52.38	$52.40	$52.40
Purchase #3	$7.53	11.512%	$8.3969	$8.40	$8.40	$8.40
Purchase #4	$87.26	13.476%	$99.0192	$99.02	$99.00	$99.00
Purchase #5	$233.68	7.185%	$250.4699	$250.47	$250.45	$250.50
Purchase #6	$108.52	8.653%	$117.9102	$117.91	$117.90	$117.90
Purchase #7	$69.71	3.180%	$71.9268	$71.93	$71.95	$71.90
7 purchase totals =	$689.72		$742.5871	$742.60	$742.60	$742.60