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	$66.78	4.534%	$69.8078	$69.81	$69.80	$69.80
Purchase #2	$82.96	10.330%	$91.5298	$91.53	$91.55	$91.50
Purchase #3	$82.67	8.781%	$89.9293	$89.93	$89.95	$89.90
Purchase #4	$208.27	6.745%	$222.3178	$222.32	$222.30	$222.30
Purchase #5	$127.67	8.492%	$138.5117	$138.51	$138.50	$138.50
Purchase #6	$175.60	6.430%	$186.8911	$186.89	$186.90	$186.90
Purchase #7	$189.45	5.190%	$199.2825	$199.28	$199.30	$199.30
7 purchase totals =	$933.40		$998.2700	$998.27	$998.30	$998.20