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	$195.34	12.356%	$219.4762	$219.48	$219.50	$219.50
Purchase #2	$56.90	10.147%	$62.6736	$62.67	$62.65	$62.70
Purchase #3	$89.97	13.403%	$102.0287	$102.03	$102.05	$102.00
Purchase #4	$142.65	6.260%	$151.5799	$151.58	$151.60	$151.60
Purchase #5	$109.29	11.607%	$121.9753	$121.98	$122.00	$122.00
Purchase #6	$63.56	6.748%	$67.849	$67.85	$67.85	$67.80
Purchase #7	$85.85	4.847%	$90.0111	$90.01	$90.00	$90.00
7 purchase totals =	$743.56		$815.5938	$815.60	$815.65	$815.60