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	$121.65	12.400%	$136.7346	$136.73	$136.75	$136.70
Purchase #2	$133.27	6.840%	$142.3857	$142.39	$142.40	$142.40
Purchase #3	$239.32	7.151%	$256.4338	$256.43	$256.45	$256.40
Purchase #4	$49.31	12.560%	$55.5033	$55.50	$55.50	$55.50
Purchase #5	$114.92	7.753%	$123.8297	$123.83	$123.85	$123.80
Purchase #6	$242.82	6.161%	$257.7801	$257.78	$257.80	$257.80
Purchase #7	$71.27	10.278%	$78.5951	$78.60	$78.60	$78.60
7 purchase totals =	$972.56		$1,051.2623	$1,051.26	$1,051.35	$1,051.20