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	$170.42	12.284%	$191.3544	$191.35	$191.35	$191.40
Purchase #2	$226.33	5.275%	$238.2689	$238.27	$238.25	$238.30
Purchase #3	$213.70	5.533%	$225.524	$225.52	$225.50	$225.50
Purchase #4	$124.98	11.650%	$139.5402	$139.54	$139.55	$139.50
Purchase #5	$121.61	12.275%	$136.5376	$136.54	$136.55	$136.50
Purchase #6	$191.30	11.335%	$212.9839	$212.98	$213.00	$213.00
Purchase #7	$157.68	8.830%	$171.6031	$171.60	$171.60	$171.60
7 purchase totals =	$1,206.02		$1,315.8121	$1,315.80	$1,315.80	$1,315.80