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	$94.69	4.562%	$99.0098	$99.01	$99.00	$99.00
Purchase #2	$231.37	8.859%	$251.8671	$251.87	$251.85	$251.90
Purchase #3	$187.67	4.750%	$196.5843	$196.58	$196.60	$196.60
Purchase #4	$97.52	8.639%	$105.9448	$105.94	$105.95	$105.90
Purchase #5	$193.78	13.597%	$220.1283	$220.13	$220.15	$220.10
Purchase #6	$81.85	4.738%	$85.7281	$85.73	$85.75	$85.70
Purchase #7	$24.34	4.835%	$25.5168	$25.52	$25.50	$25.50
7 purchase totals =	$911.22		$984.7792	$984.78	$984.80	$984.70