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	$99.42	3.365%	$102.7655	$102.77	$102.75	$102.80
Purchase #2	$216.36	3.800%	$224.5817	$224.58	$224.60	$224.60
Purchase #3	$189.71	7.699%	$204.3158	$204.32	$204.30	$204.30
Purchase #4	$90.93	10.139%	$100.1494	$100.15	$100.15	$100.10
Purchase #5	$55.94	10.752%	$61.9547	$61.95	$61.95	$62.00
Purchase #6	$119.67	9.586%	$131.1416	$131.14	$131.15	$131.10
Purchase #7	$101.95	12.739%	$114.9374	$114.94	$114.95	$114.90
7 purchase totals =	$873.98		$939.8461	$939.85	$939.85	$939.80