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	$38.50	4.253%	$40.1374	$40.14	$40.15	$40.10
Purchase #2	$67.46	10.871%	$74.7936	$74.79	$74.80	$74.80
Purchase #3	$153.61	10.352%	$169.5117	$169.51	$169.50	$169.50
Purchase #4	$6.96	9.456%	$7.6181	$7.62	$7.60	$7.60
Purchase #5	$102.36	8.805%	$111.3728	$111.37	$111.35	$111.40
Purchase #6	$137.49	13.150%	$155.5699	$155.57	$155.55	$155.60
Purchase #7	$115.51	12.553%	$130.01	$130.01	$130.00	$130.00
7 purchase totals =	$621.89		$689.0135	$689.01	$688.95	$689.00