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	$20.86	3.363%	$21.5615	$21.56	$21.55	$21.60
Purchase #2	$241.45	10.793%	$267.5097	$267.51	$267.50	$267.50
Purchase #3	$198.48	7.106%	$212.584	$212.58	$212.60	$212.60
Purchase #4	$243.90	3.742%	$253.0267	$253.03	$253.05	$253.00
Purchase #5	$174.88	4.347%	$182.482	$182.48	$182.50	$182.50
Purchase #6	$217.50	4.556%	$227.4093	$227.41	$227.40	$227.40
Purchase #7	$81.68	10.670%	$90.3953	$90.40	$90.40	$90.40
7 purchase totals =	$1,178.75		$1,254.9685	$1,254.97	$1,255.00	$1,255.00