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	$45.73	10.193%	$50.3913	$50.39	$50.40	$50.40
Purchase #2	$59.85	3.278%	$61.8119	$61.81	$61.80	$61.80
Purchase #3	$198.39	10.138%	$218.5028	$218.50	$218.50	$218.50
Purchase #4	$164.66	12.404%	$185.0844	$185.08	$185.10	$185.10
Purchase #5	$166.65	4.757%	$174.5775	$174.58	$174.60	$174.60
Purchase #6	$250.45	9.524%	$274.3029	$274.30	$274.30	$274.30
Purchase #7	$138.72	12.570%	$156.1571	$156.16	$156.15	$156.20
7 purchase totals =	$1,024.45		$1,120.8279	$1,120.82	$1,120.85	$1,120.90