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	$112.98	3.426%	$116.8507	$116.85	$116.85	$116.90
Purchase #2	$164.25	4.338%	$171.3752	$171.38	$171.40	$171.40
Purchase #3	$156.70	6.314%	$166.594	$166.59	$166.60	$166.60
Purchase #4	$134.73	12.187%	$151.1495	$151.15	$151.15	$151.10
Purchase #5	$33.67	6.516%	$35.8639	$35.86	$35.85	$35.90
Purchase #6	$82.45	8.842%	$89.7402	$89.74	$89.75	$89.70
Purchase #7	$92.93	11.701%	$103.8037	$103.80	$103.80	$103.80
7 purchase totals =	$777.71		$835.3772	$835.37	$835.40	$835.40