Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$98.45	13.585%	$111.8244	$111.82	$111.80	$111.80
Purchase #2	$128.61	5.537%	$135.7311	$135.73	$135.75	$135.70
Purchase #3	$17.35	4.499%	$18.1306	$18.13	$18.15	$18.10
Purchase #4	$151.28	3.584%	$156.7019	$156.70	$156.70	$156.70
Purchase #5	$93.30	4.365%	$97.3725	$97.37	$97.35	$97.40
Purchase #6	$35.47	5.819%	$37.534	$37.53	$37.55	$37.50
Purchase #7	$212.67	4.622%	$222.4996	$222.50	$222.50	$222.50
7 purchase totals =	$737.13		$779.7941	$779.78	$779.80	$779.70