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	$238.67	11.671%	$266.5252	$266.53	$266.55	$266.50
Purchase #2	$120.42	5.832%	$127.4429	$127.44	$127.45	$127.40
Purchase #3	$93.34	9.800%	$102.4873	$102.49	$102.50	$102.50
Purchase #4	$168.58	12.393%	$189.4721	$189.47	$189.45	$189.50
Purchase #5	$90.68	9.633%	$99.4152	$99.42	$99.40	$99.40
Purchase #6	$11.67	13.873%	$13.289	$13.29	$13.30	$13.30
Purchase #7	$68.71	12.595%	$77.364	$77.36	$77.35	$77.40
7 purchase totals =	$792.07		$875.9957	$876.00	$876.00	$876.00