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	$127.90	7.509%	$137.504	$137.50	$137.50	$137.50
Purchase #2	$200.56	13.546%	$227.7279	$227.73	$227.75	$227.70
Purchase #3	$150.82	11.482%	$168.1372	$168.14	$168.15	$168.10
Purchase #4	$48.47	11.258%	$53.9268	$53.93	$53.95	$53.90
Purchase #5	$102.90	10.646%	$113.8547	$113.85	$113.85	$113.90
Purchase #6	$96.93	5.655%	$102.4114	$102.41	$102.40	$102.40
Purchase #7	$91.65	6.669%	$97.7621	$97.76	$97.75	$97.80
7 purchase totals =	$819.23		$901.3241	$901.32	$901.35	$901.30