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	$43.94	12.742%	$49.5388	$49.54	$49.55	$49.50
Purchase #2	$130.71	8.179%	$141.4008	$141.40	$141.40	$141.40
Purchase #3	$166.43	11.577%	$185.6976	$185.70	$185.70	$185.70
Purchase #4	$73.62	13.506%	$83.5631	$83.56	$83.55	$83.60
Purchase #5	$215.87	10.298%	$238.1003	$238.10	$238.10	$238.10
Purchase #6	$204.62	8.305%	$221.6137	$221.61	$221.60	$221.60
Purchase #7	$35.63	4.216%	$37.1322	$37.13	$37.15	$37.10
7 purchase totals =	$870.82		$957.0465	$957.04	$957.05	$957.00