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	$47.86	4.190%	$49.8653	$49.87	$49.85	$49.90
Purchase #2	$215.75	11.212%	$239.9399	$239.94	$239.95	$239.90
Purchase #3	$169.95	9.212%	$185.6058	$185.61	$185.60	$185.60
Purchase #4	$68.78	13.616%	$78.1451	$78.15	$78.15	$78.10
Purchase #5	$109.77	9.853%	$120.5856	$120.59	$120.60	$120.60
Purchase #6	$209.94	10.257%	$231.4735	$231.47	$231.45	$231.50
Purchase #7	$29.75	13.217%	$33.6821	$33.68	$33.70	$33.70
7 purchase totals =	$851.80		$939.2973	$939.31	$939.30	$939.30