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	$238.73	13.596%	$271.1877	$271.19	$271.20	$271.20
Purchase #2	$72.52	7.687%	$78.0946	$78.09	$78.10	$78.10
Purchase #3	$72.91	11.520%	$81.3092	$81.31	$81.30	$81.30
Purchase #4	$74.71	8.167%	$80.8116	$80.81	$80.80	$80.80
Purchase #5	$235.33	11.639%	$262.7201	$262.72	$262.70	$262.70
Purchase #6	$59.88	9.179%	$65.3764	$65.38	$65.40	$65.40
Purchase #7	$44.80	3.456%	$46.3483	$46.35	$46.35	$46.30
7 purchase totals =	$798.88		$885.8479	$885.85	$885.85	$885.80