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	$34.91	10.205%	$38.4726	$38.47	$38.45	$38.50
Purchase #2	$65.83	12.168%	$73.8402	$73.84	$73.85	$73.80
Purchase #3	$93.46	6.752%	$99.7704	$99.77	$99.75	$99.80
Purchase #4	$160.55	3.546%	$166.2431	$166.24	$166.25	$166.20
Purchase #5	$82.67	6.713%	$88.2196	$88.22	$88.20	$88.20
Purchase #6	$145.48	8.244%	$157.4734	$157.47	$157.45	$157.50
Purchase #7	$126.84	12.627%	$142.8561	$142.86	$142.85	$142.90
7 purchase totals =	$709.74		$766.8754	$766.87	$766.80	$766.90